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MG MGB Technical - Weber carb problem 2

I have a weber 32 36 dgev - 77 mgb roadster.
Problem is adjusting mixture at idle and gas readout at 9%. Adjusting the idle mixture screw either way makes no difference to engine idle or emmision percent. The engine is nice and warm.
Have serviced the carb including new accelerator pump and power valve. The floats are correct at 41 mm plus movement of 10 mm. Another problem is that the engine does not pull very well. As though there is no 'power' - but this could be timing on the dis (45d) and a punctured vacum unit and nothing to do with carb setup.
My logic says that carb cannot be too rich as gas reading says 9%.
I have disconncted the choke function and have the two barrels fully open.
Any suggestions would be much appreciated as it is driving potty...
/Moss
Moss

Is that a CO reading of 9%? That is hugely rich, should be around half that.

Are you running this with a punctured vacuum unit? That's asking for problems, fix faults first.
PaulH Solihull

Paul, yes, CO at 9 %. I meant of course that it is too rich. Do not know if vacum unit is punctured...
/Moss
Moss


If you can suck air through the line to the vac advance, it is bad. If you cannot, then take the cap off and watch the points plate to see if it moves when you suck (hard!). Or pull the line off with the engine running while watching the timing light/mark; with manifold vac as you should have, the timing should advance when the line is connected and retard when disconnected. Then set the timing correctly. Carb fine tuning is the LAST thing you set, after timing and valves and plugs etc.

All that notwithstanding, if the idle screw does nothing, then there is likely a fault in the carb idle circuit.

FRM
FR Millmore

Moss. High carbon monoxide (CO) readings are due to inefficient burning of the fuel air mixture. They can be seen both when the mixture is excessively rich and when the mixture is excessively lean because neither burns efficiently.

If you are running a Weber DGV series carb on a rubber bumper car, what has been done to the exhaust system to adapt the one piece intake/exhaust manifold to your new intake manifold and carb? Are the flanges of the intake and exhaust manifolds the same thickness? If not, have they been shimmed so that all of the flanges seal properly to the manifold gasket? Air leaks around the two legs of the intake manifold result in a leaner mixture which, in turn, can result in "lean miss" which will not burn efficiently.

What happens to the CO readings when you spray some carb cleaner around the base of the carb and along the gasket surfaces? What happens to the CO readings when you run the engine up to about 3,000 rpm? The reading should go up, then drop down to about 5% range at steady state operation.

I agree with Paul and Fletcher that the ignition system must be in excellent condition if you are to do any carb tuning. Improper timing and any distributor problems can cause improper burning of the fuel/air mixture which will give you high CO readings. Only when the ignition is properly set up can you dial in the carb accurately.

Are you using a gunson's CO meter? The two I have owned were wildly inaccurate when compared to professional grade instruments owned by professional mechanics and the state emissions inspection stations. Sufficiently so that mine has been used as a paper weight for the last ten years. A cross check of the test equipment might also be in order.

Les
Les Bengtson

Les and others, re: my first thread about carb. Have now discovered that the power valve diaphragm is brittle (I was checking for puncturing)thereby the spring face is pushing down all the time on the full power needle - no vacum holding it up. Therefor too rich and no adjustment on the mixture screw. Thought I had ordered the correct one through e-bay but something went wrong - so have now ordered again and correct this time - confirmed!

The CO at 9% was determined by a garage. I pressume this is accurate enough.

Re: vacum advance unit on dis. When I blow or suck hard on the tube going to the vac unit there is a popping sound in the vacum advance unit - is this normal?

The not so easy task:
The crankshaft pulley has no timing marks!

/Moss

Moss

Popping sound - not normally, it should move the arm coming out of the diaphragm that is connected to the points plate so twisting it back and fore. Something could be sticking slightly, or it may just be the sound of the points plate moving. As long as the points plate twists clockwise when you suck (you need to suck hard, probably with your mouth rather than your lungs), and returns when you release the suction, and you can't suck (or blow) air continually through the diaphragm, it is fine.

Timing mark - are you sure it isn't filled with dirt? If there really is no timing mark (notch) you will have to make one. For this you need something projecting into No.1 cylinder through the plug hole, such that it stops the piston shortly before it reaches TDC. It either needs to be fixed so it can't move, or you need to use a depth gauge through the plug hole. Turn the crank one way (all plugs out makes it easier) until the top of the piston just touches the stop or depth gauge. If the latter note the reading. Make a mark on the pulley in line with the TDC pointer on the front cover (I assume you have those marks!). Now turn the crank backwards until the piston goes down and comes back up again, and again just touches the stop, or until you get the same reading on the depth gauge as before. Make a second mark on the pulley again in line with the TDC mark. True TDC on the pulley lies exactly between your two marks.
PaulH Solihull

Have now checked vacum advance - working fine. Took the distributor cap off - could see the base plate moving in time with the suction. However, I think the points need a service ie. replacing. I have had a leaking heater valve (now replaced)and the water has leaked down onto the dis and inside the body of the dis. The inner wall has a layer of dried something or other on it. Cannot be optimal for system! And whilst I'm in the process will do the timing (first time for me)

Should I just replace the points or go over to electronic?

The crankshaft pully is very very rusty - therefore timing marks have eroded away.
/Moss

Moss

Moss. Remove the V belt from the water pump, harmonic balancer, and the alternator. Use a wire brush on the circumference of the harmonic balancer, rotating the balancer as needed to allow you to brush the rust off the edge. You should be able to make out the mark, which runs fore-aft, as there will be less rust removed in that area. Paint the now visible line with a light colored paint and you have your timing mark.

A points system will be easier to trouble shoot. An electronic points replacement system will cover up some distributor problems, making them no longer an issue. However, when installing a points replacement system, it is most successful when used with a rebuilt distributor. But, then, so are new points.

When installing new points, or a points replacement system, it is best to remove the distributor from the engine--makes it much easier to work on. Also, allows you to remove the points plate, clean and lubricate the inside of the dizzy and the points plate. That will make the assembly work in a more consistent manner.

I would, myself, install a new set of points and make a final decision after the engine is properly set up. Otherwise, you are simply adding one more variable to your trouble shooting problems right now.

Les
Les Bengtson

Hi Les, had not thought of the rust removmal! Very good idea...thanks. I forget sometimes that solutions to problem can often be very simple.
Re points, will go for the points renewal instead of new electronic system at this stage. The dis is a 45D. The plate and other parts inside are still very shiny so po probably not very old at all. There is also the cost issue (for me, anyway)...

Taking out the dis is daunting but I know it has to be done. Only two bolts but is it not very tight in the engine block? I have read up on how to do and sounds very easy but...

/Moss


Moss

Hi again, trying to remove the dis, however, will not retract from the engine block! Engine at TDC - rotor arm and therefore spindle pointing at nummer 1 spark plug (if one can put it like this) Am I missing something? Am I being too gentle ie, give it a whack with the hammer...
Any suggestions much appreciated.
/Moss
Moss

That's bad, but you have to get it out, as it must be turned to set timing. A good penetrating oil around the distributor base, time, lots of effort twisting and pulling. NO HAMMER!

FRM
FR Millmore

Of course, no hammer! Could it be that I need to set the dis at 7 degrees BTDC? I ask because my engine code (18V 846) dictates that static timing has to be at this setting and not at TDC. Therefore my logical thinking tells me the dis has to positioned like this as well before taking it out. To be honest I undertand the theory but in reality I'm having trouble visualising where the 'dog' pin at the end of the spindle of the dis is sitting in the engine block...
/Moss
Moss

Where the engine is when you remove the dist doesn't matter, though it is convenient to have it near TDC. The offset dog on the shaft means the shaft will be in the correct position when you refit the dist, else it will not go home all the way. The actual timing is set by turning the dist body, which changes the relationship of the spark generating bits relative to the shaft. That's what determines timing. Since you are going to fiddle with the innards, the timing will be different when you put it back, so there's no reason worry about exact position on removal.

FRM
FR Millmore

The only time you set the *distributor* to TDC is when timing something like the 123. As FRM says you don't need to set the crank to TDC to remove (or insert) the distributor, it should come out in any rotational position of the crank, cam or drive-dog. The key and keyway are positioned on the end faces of the distributor and drive dog shafts, not in line with them like between the crank pulley and the crank. Likewise you don't have to worry about turning the distributor or the engine while the engine is out, simply turn the *rotor* while applying gentle pressure pushing the distributor into the block, and it will drop into engagement in the correct position. You will still have to static time it before starting though unless you use match-marks, which should allow you to start it and then dynamic time it. Note that the key and keyway are very slightly offset so that it *does* only fully slot in in the correct position, but the offset is so small that when it is 180 degrees out it may well feel like it wants to go in, but won't fully. If you find that simply turn it 180 degrees and try again.

Note also that if you dismantle the distributor i.e. part the two halves of the shaft involved with centrifugal advance e.g. to get at the springs and weights, it is possible to reassemble them 180 degrees out. This will put the rotor in the wrong position for the leads in the cap, unless you shuffle them round to suit.
PaulH Solihull

FR and Paul, thanks for advice - now I'm starting to understand. Have now put pen.fluid around the dis./engine block, bought my timing light/gun. Very excited about doing the timing. I have a feeling the timing is out - engine has never 'felt' smooth enough.
I checked the spark plugs yesterday and they are all very dry poweder black. They were not last season - have driven 100 km this year (since february 19th) so something very very wrong (the carb problem).
/Moss
Moss

Advice much needed. Still cannot move the dis - will not even twist with the clamp plate very loose. Where and what could be holding it solid? Cannot be the spindle as this turns as it should (ie., in gear pushing car forward can see the rotor arm moving round...)
/Moss
Moss

Moss. First, the distributor problem. The distributor body has, most probably, become corroded (oxidized--e.g. rust on steel) and this is jamming together the aluminum body of the distributor and the iron/steel body of the distributor housing.

The distributor housing is a bushing which fits into the hole on the side of the engine and holds the distributor drive in place. The distributor goes into the distributor housing and engages the distributor drive. The distributor housing is held to the block by a single screw. I do not know if you can get to this single screw and remove it with the distributor in place. If you can, it would allow you to remove both pieces and soak them in a container of oil, then separate the two pieces.

The fact that the distributor cannot be rotated indicates that the ignition system cannot be timed and is, most probably, out of time now. High CO numbers and black soot on the spark plugs indicate that the fuel/air mixture is not burning efficiently and generating a lot of byproducts in that inefficient burning. Both excessively lean and excessively rich mixtures can have these symptoms. And, so can an engine seriously out of time--even with the correct fuel/air mixture.

I consider the problem you are having with your distributor may well have a quite significant impact on your "weber carb problem", even if you have found the accelerator pump and power valve to be bad. The fact that replacing these parts has not corrected the problem might well indicate that, while they were bad and did need to be corrected, they were not at the root of the problem.

Without all of the various systems (carb, ignition, exhaust, pollution control--if fitted, etc.) being in working order it is difficult to diagnose and correct problems. Hence, you have committed yourself to the quite interesting (and frustrating) job of finding and correcting an interconnected series of problems. All in hopes that, when you have corrected them, the engine will be in good condition and capable of being properly tuned and used for several years.

Were I ten years younger, I would envy you. I did the same thing, several times, and got a great feeling of accomplishment by doing so. Plus, I learned a great deal about engines and myself. Today, however, I would swap in a good condition, running engine.

It may be time to start a new thread about how to remove a stuck distributor. We last discussed this several years ago and the thoughts should be in the archives. But, there are other people here today who may have other, perhaps better, thoughts on how to do this--perhaps some that will work for you.

Les
Les Bengtson

Moss-
Exactly as Les said.

Everything needs to be soaking in penetrating oil while you do the following. Worth heating the base of the distributor up gently and letting it cool a few times. That should help the oil get in there.

You can leave the clamp plate bolt snug, and drive thin wedges under the plate from two sides to put substantial upward force on the distributor. You have to be careful about breaking the shoulder of the distributor, which is why you use force under the plate with the bolt in place, not on the distributor.
Then try twisting the distributor.

You can remove the clamp bolt and turn the plate to see if you can get the single screw out that retains the housing, as Les said. I think the plate will still be in the way. Some amount of distorting the plate may be necessary, up to cutting it off. But the plate should be easily available and cheaper than a distributor.

Once you get the housing/dist out, figure out how to support the housing, heat it up with a propane torch, and drive the distributor out from the bottom end.

FRM
FR Millmore

Hi Les og FR, many thanks for comments and advice - phew!
Now I know what I will be doing at the weekend...I'll update soon
/Moss
Moss

Still cannot get the dis out!
However, have now used a hammer and a flat ended chisel on the shoulders of the clip mounts (for the dis cap) I know not a wise thing to do. It moves round slightly but not enough. I have thought about taking the vacum advance unit off so I can use an oil cannister 'wrench' on the body of the dis but cannot see the screw that holds the end of it to the mechanism in the dis.

Any suggestions?
/Moss
Moss

Moss-
If it moves at all, you are on the way to success!
More penetrating oil and twist/pull/swear/hurt hands, repeat.
Possibly a loop of nylon rope around the advance, to a bar, can be used as a wrench.

FRM
FR Millmore

FWIW Once you have the screw out that hold the vacuum capsule to the outside of the distributor the business end hooks on to a pin to rotate the points plate. If nothing else removing the points plate (two screws) will detach that from the vacuum unit, then that unit can be removed.

But as FRM says if it is moving at all then it is on its way, patience and perseverance.
PaulH Solihull

At last the dis is out. What a relief. Can see the cause of the problem. The heater valve had been leaking (now renewed) and the fluid had been leaking down onto the dis - corrosion around the shoulder of the bit the goes into the block. Therefore very tight. Wire brush to remove the white/blue crud...

Now whilst the dis is out time for a service....shall I replace the points with electronic module or...? :) Don't bother to answer as I can read the other thread about this...

Still have the carb problem to sought out (CO at 9%) but that's another story...perhaps the correct timing will help. On the timing gun the red lead goes to the bottom fuse but where is the best place to 'ground'?

Thanks for all the help....again again
Best to all
/Moss
Moss

Moss. Until the distributor is in good working condition and the engine is timed properly, you do not know if you still have any carb problems. Ignition timing is also a factor in the CO readings. And, if you are simply using a cheap CO meter (like the Gunson's) you do not have the other readings that the four and five gas analyzers provide to tell you what the real problem is.

For the distributor, the first thing to identify is what model you have. Probably a Lucas 25D4 or 45D4 as these were the two points type distributors used with the MGB. However, the Lucas DM2 distributor, used in the MGA, will also fit into the hole in the engine and work. So, clean up the body of the distributor with a wire brush and see what markings are on it. The two most important are the model number and the specification number. The model number tells you what parts are needed (e.g. correct rotor, points, condenser, and distributor cap) while the specification number may tell you the expected mechanical curve and vacuum advance specifications. I say may because that would require the distributor be in good working condition and never rebuilt.

The second thing I would do with the distributor is take it apart, thoroughly clean it, inspect it, lubricate it, then reassemble it. I would install points until you get the engine fully operational and all the problems sorted. At that point, you can decide if you want to go with a points replacement system. But, remember, the distributor is still designed to be lubricated on an annual basis, regardless of the coil triggering system installed, and lack of lubrication can cause functioning problems.

Les
Les Bengtson

Hi Les, the dis is a 45D4 number 41610D 2500. I doubt that it is original as the vacum advance unit, under the dirt,still has the brass colour which I can see on pictures of ones one can buy via net shopping. And the points are not very warn - still silver coloured.

I am also uncertain of the timing specification. The engine is a reconditioned unit by an English company (Ivor Searle); It was done in 2008 (I bought the car in June 2010) and according to them the spec. is as 18V 846F. So according to the manual 7 degrees static and 10 degrees at 1000 rpm. However there are things about the engine which puzzle. The emission control bits are removed (the car did have a Stromberg - there is a sticker with timing and emission details in the engine bay). There is no catalytic converter and the engine block breathing is through the side cover and pipe - when I got the car the pipe was not connected to anything and just open; I have since fitted a filter on the end. Now it does not smell of fumes any more!!

So the question is do I stick to the 846F timing spec, hoping that it is correct, or is there another sure way of finding the correct timing? Basic question perhaps but is it the dis that decides the timing or the engine build which the dis then has to be matched.

By the way I've read your monologue on ignition timing - very useful.

/Moss


Moss

18V 846 was a high compression, not North America i.e. UK, so shouldn't have had the Stromberg or any of the emissions kit including catalytic converter. The engine side cover should be connected via a Y-pipe to the PCV vents on the carbs for suction, which should be HIF on the 846. HS and HIF carbs (and the Stromberg for that matter) from 1968 had these ports, what carbs do you have? The oil filler cap should be the filtered and restricted fresh air inlet. With just a filter on the side cover you have no crankcase ventilation, so can get internal condensation and corrosion. If the car was originally an American spec, and the UK engine was transplanted in, then that would explain the engine bay stickers. According to my info this engine did originally have the 45D4 41610, and has the timing info you give, but that was on leaded 99 point something octane fuel. As with virtually any HC MGB these days you have to set the timing so it doesn't pink at any combination of revs, throttle opening or load with the fuel you normally use. Even with 99 octane V-Power I can't get mine to run at original manufacturers timing figures, I have to retard it slightly.
PaulH Solihull

The car is originally US spec - I have three window wipers for example and of course left hand drive. The engine must be an implant, probably an exchange unit - who knows - the engine code has been replaced by Ivor Searle's own. The carb on now is a Weber 32 36 DGEV - a usual replacement for the Stromberg I'm pretty certain.

/Moss
Moss

OK, fixed jet carbs don't have the PCV port, so you need to fit a PCV valve to the inlet manifold as per the earlier arrangement and plumb that to the front tappet chest. Assuming the inlet manifold has a suitable tapping of course!
PaulH Solihull

Paul, It has not - instead a pierce inlet manifold for the Weber - the 'tap' is for the vacum to the Bendix brake servo unit...obviously the complications continue...although many late rubber bumper MGBs have converted to the Weber...more research required on my part...
/Moss
Moss

Moss. The simplest system is to get an air filter housing that has a hole for a 90 degree elbow. A plastic elbow, supplied with the air filter, fits into the hole and is connected to the hose coming from the front tappet cover. Have used this system on three cars with good success. The Weber DGV series carbs were often used as conversions on the old Volkswagen "Beetle" cars and there are many Volkswagen accessories available for the DGV carb. I purchased my air filter at a local VW specialist shop.

Les
Les Bengtson

Problem with the method Les describes is that the PCV system is no longer "Positive"
You can tee at the servo take off and connect PCV valve there.

FRM
FR Millmore

Hi Les, sounds like a good idea - on the base-plate of the carb where the carb air filter sits there is a whole. I've seen pics where this is connected up via a pipe/tube to the front tappet pipe cover. Looks very simple but effctive...Fr, thanks for advice, I'll save that for a rainy day - not quite understood the pcv positive system yet - more reading to do.

Still waiting for my parts from UK (new dis cap, leads and plugs), been 10 days now...hopefully soon. Cleaned and serviced the dis - looks good and the mechanisms seem smooth and functional - adjusted the points, they were at 0.017 inch.

Problem with putting dis back in - Cannot seem to be able to insert all the way down. I can exchange the dog but won't go down the last inch or so. Could this have something to do with the compression stroke of the engine ie. I need to turn the engine a full cycle again?
/Moss
Moss

"the PCV system is no longer "Positive""

Indeed, that is the system the factory used for a short time, and it is a matter of conjecture whether filtered or unfiltered air flows into the crankcase, or nothing at all.

The problem with Teeing off the servo hose is that it will remove the residual vacuum in the servo if the engine stops spinning while you are still under way. Ordinarily the one-way valve in the manifold port stops this happening, and leaves you with a few assisted pedal operations. Not an issue with the earlier remote servos as they only gave very light assistance, but I understand it is significant on the later master with integral servo. If the one-way valve were on the servo it wouldn't be a problem.
PaulH Solihull

I meant of course 'engage the dog' not exchange....
Paul, no comment on your PCV input, not understood the system yet....have to read your website article :)

Any comments on inserting the dis from anyone would be much appreciated...
/moss
Moss

It worked - the engine was not at the compression stroke, turned one revolution and went down in the slot very easily...just have to connect all the bits and then time the engine...
/Moss
Moss

""the PCV system is no longer "Positive""

Indeed, that is the system the factory used for a short time, and it is a matter of conjecture whether filtered or unfiltered air flows into the crankcase, or nothing at all."

Factory systems with air filter vent take offs used a road draft tube, and filtered air flows into the engine and out the tube. Except at rest, when it could go into the carbs, there being no "road draft" present.

"The problem with Teeing off the servo hose is that it will remove the residual vacuum in the servo if the engine stops spinning while you are still under way. Ordinarily the one-way valve in the manifold port stops this happening, and leaves you with a few assisted pedal operations."
All true. The arrangement needs to be such that the check valve is between the manifold/PCV tapping and the servo. Something I can't recall had a banjo fitting for the PCV under the manifold mounted check valve, or there are line mounted checks, or servo mounted ones.

Moss is going to be a real mechanic when he gets this thing working - keep it up!

FRM
FR Millmore

The car runs - started first time! So my static timing skills are now in place! However, now a new problem. Cannot get the timing light to work...attached the red clip to bottom fuse terminal and black clip to metal in the engine compartment - but no light! Apart from the obvious ie., bulb broken in the gun, what could be the problem?
Advice appreciated...

/Moss
Moss

Silly me! I had connected the red clip incorrectly. Timing gun works perfectly - however, the dis does not. Very jerky movements at the 10 deg. dynamic. According to my Haynes manual this means the dis and/or the timing chain is worn....does this mean new dis or is there a clever way to compensate for the wear? l'll start a new thread.
/Moss
Moss

Could be stretched springs in the distributor. Remove the cap and manually turn the rotor anti-clockwise against spring pressure. Slowly release it, and it should return all the way with no slop when fully released. However some slop is inevitable in a used distributor, it all depends how much you get.
PaulH Solihull

Well the carb problem is not a carb problem at all! No, the problem has been an inexperienced amateur home mechanic! The idle mixture screw was not all the way in. Half an inch to be exact - this is why no difference when turned in or out. I've been too cautious. New screw with a tight thread so have been wary. Took the carb off the manifold and measured length of screw in relation to in place in the carb base and found no where near enough screwed in. Hence full flow of fuel going in, no pressure build up, so no vacum holding the power valve diaphram up off the power valve - hence down on the pin allowing fuel from the float bowls at constant flow and the idle 'chamber'....on the positive side found out the carb positioned incorrectly on the inlet manifold - better placed 180 degrees round, all the adjustment screws and choke have faced the rocker cover - know have to buy new lead for the electric choke and vacum advance tube so it can reach the new position - easy stuff even for me...I hope :)
/Moss
Moss

Moss,

Good find on both parts. Shouldn't be long till it's running sweet.

Charley
C R Huff

Thought it would run sweet...but still the same b..... problem. Now I can turn the idle mixture screw all the way in and it should be so rough due to petrol starvation but no, starts fine, runs well but now my new spark plugs after 22 miles are dry powder black! Something is making the petrol by-pass the idle mixture screw...

Help!
/Moss
Moss

Moss,

In your first post you said you serviced the carb. Did you fully disassemble it, clean it, and rebuild it with a new kit? If not, maybe you should.

Also, I don't think you ever answered the question from Les on April 3 about the manifolds. Better look into that if you haven't already.

Charley
C R Huff

The carb has been taken apart - in two halves, the floats, gaskets, needle valve, accelerator pump and power valve have been replaced and the unit cleaned, I would not say stripped! Have checked the inlet and outlet manifolds (sorry Les for not confirming)they are flush. But I cannot understand how these would effect the idle mixture screw - if excess air getting in then mixture would be lean, would it not?

The problem is too much petrol (show on the gas tester at 9% and powder black plugs) and the total lack of adjustment on the the idle mixture screw.
/Moss
Moss

Do some research on tuning your downdraft. See what your jet settings should be and buy the proper jets to get you in the ball park and tune from there. When you buy a downdraft it could have any jets fitted as they can be used for a ton of different vehicles. The most important thing is you got your timing set! Do a search and you can find peoples jet settings etc and swap out the ones you have. You should get into the ball park and then fine tune from there.

I say stick with the downdraft and get it tuned. Ive switched out sooo many carbs etc and found SU's are for me but you have something that will work well. Get it tuned and running... and then if you ever get curious after a summertimes worth of use, have fun in the winter time with trying a sidedraft or su's...

If you need help let me know...

-James
JRB Mr

Hi, thanks for imput. It really is a puzzle. I must be overlooking something. I have followed all the procedures, have checked the jets etc. They are standard.
I have taken the carb off twice over the last two weeks to check if I have missed something. The timing has been tripple checked, including the advance and the vacum unit. But still no idle mixture screw adjustment possible.
The thing is, the car starts without any problem and since doing the timing the car does run better. Only my new plugs powder black after only 22 miles!

I'm going to get a new reading done on the CO emission from a garage...and turn the screw in and out to see if it does in fact make a difference. Perhaps a really really long run will help - I have been letting it tick over for longer than is possibly wise whilst I've been doing all this fiddling!


Moss

what do you mean by standard jets? Seems you need to go smaller on your main jet.
JRB Mr

Moss,

I don't claim much knowledge of those Webers, but I have tried partial disassembly and cleaning of what I thought were the most important parts of a carb, and then not gotten the result I was hoping for.

Sometimes that works, but sometimes only a full teardown, soaking in carb cleaner, blowing out with compressed air, and a rebuild kit will do the trick.

Charley
C R Huff

Moss. When you remove the top cover, there are two jets (small, brass things with a hole in the center and a slot for a common screwdriver) visible. Each jet has a number stamped on it. You need to see what those numbers are and post them. I have found quite a number of different jets in these carbs over the years, all of which claimed to be suitable for the MGB. Sometimes, I had to change out the jets to get the car to run properly.

As Charley suggests, a complete removal of the carb and a good soaking in carb cleaner is not a bad idea. There are a number of hidden passages within the body, all of which need to be completely clean before proper tuning can take place.

Yes, it would be a good idea to have your meter cross checked with one of professional quality. I have tried to use the Gunsen's CO meter but, when compared to a professional meter, the Gunsen's readings were wildly inaccurate. May be the pollution level where I live or it may be the meter is not all that good. Professional grade meters are far more expensive, have to have certain parts replaced on a regular basis, and have far higher accuracy standards.

The importance of the flanges of the intake manifold and exhaust manifold (or header) being the same is that, if they are not, the two may not seal correctly to the manifold gasket, allowing air leaks which effect the ability to tune the carb. Spraying carb cleaner around the carb and the intake manifold while the engine is running is a good test for air leaks. If the idle speed changes there is an air leak which is being temporarily sealed by the carb cleaner.

Les
Les Bengtson

yea back when I had one on mine I had to make up a special bracket to even the difference in intake and manifold thickness so they can torque down correctly.
JRB Mr

JRB you are right, I walked into that one - what I meant by standard was the sizes that are stipulated on the diagram in the kit I got. Of course it is a tuning device so jets and tubes can be changed to different sizes dependent on engine.

Les, I'll have a look tomorrow...
/Moss
Moss

Did you check the power valves? I may have missed it in this long thread. If so I apologize.

A bad diaphragm or leak on a power valve will make for a very rich mixture. I don't know if they affect the idle circuits however. I don't think they are part of the standard rebuild kit but are easy enough to source.

I seem to remember a thread not too long ago about a DGV running quite rich. Turned out it was bad power valve.

Bob



Robert McCoy

Moss-
What was that about the idle mixture screw, 10 May?

FRM
FR Millmore

Joy of joys...the mixture screw adjustment is working. The only thing I've done is removed the new spring that fits around the mixture screw to give tension so it could go in further. And whoopty adjustment possible. The odd thing is that the new spring is as long as the old spring.

Adjusted as per instructions (1. 5 turns out and idle at 800 rpm)and it turns over fairly smoothly but acceleration is poor. Yes, I have replaced the accelerator pump (the old was very worn)and the power vavle and power valve diaphram

Will check timing again...

/Moss
Moss

Buy some jets, have some fun! Best of luck !
JRB Mr

Indeed...but then that begs the question 'what jets does one buy?'...no comments please! I have enough difficulty finding out how the carb works with the existing jets!

Thanks for all the input from everybody. I have learned alot again...til next time and another problem!
/Moss
Moss

Update - the timing was out - dynamic timing was at 8 deg BTDC (at 1000 rpm with vacum advance tube disconnected)instead of 10 deg stipulated by the spec.
The clamp plate must have been loose.

...And discovered something even more 'silly'! The throttle cable has been connected incorrectly. I have never thought it was an issue! Was looking down the ports while operating the throttle mechanism and noticed that... believe it or not... the full cycle of the throttle mechanism was not operative. The second throttle valve (not choke valve),which is supposed to open at 2/3 acceleration, was staying shut. So not a surprise that I have felt the engine never has had enough power.

Did the timing at what a difference - the car sounds throaty and acceleration is much better - however, a flat spot when second throttle opens and more fuel gets pumped in. My assumption is that the extra fuel is not being burned - as though the ignition system cannot cope with the extra fuel being pumped in while accelerating. Then when engine turned off there is 'run on' for a few seconds.

I am using V power 99 octane.
/Moss
Moss

You'd be surprised at how many cars I've seen not getting full throttle, even after the owner bought it new and drove for several years. I've had a number of people return or call after a correct tune to ask "What in the H*** did you do to my car? It never went this fast!"

A carb with secondaries is even worse on this. Your stumble when the secondary opens is almost certainly not enough fuel from the pump circuit, or and/or overall lean condition at primary mid range. There is normally an adjustment or part change to tune the accel pump circuit, but I am not familiar with that carb.

Run on is normally due to too fast idle speed.

FRM
FR Millmore

Hi FR, thanks for your comments. If too lean perhaps the mixture screw problem is not solved yet. I have replaced the accelerator pump - it was very worn down (the 'finger' which presses in). There is no adjustment possible - I have the DGEV.
/Moss
Moss

Moss-
The thing with fixed jet carbs is that there are different circuits affecting mixture under different speeds and conditions, but all interacting to varying degrees.

Your idle mixture screw should not have much influence at the point the secondary opens. This would be the region of mid range to high speed jetting. I just don't know enough about this carb to tell you what exact things to look at, nor any pics, diagrams etc.

Accel pump action is usually adjusted by either linkage (pump actuator arm or cam), or pump spill restrictors inside. Also possible that there are different pump nozzles. If some part of this linkage was worn, whatever contacts it may be as well.

Mid range jetting frequently involves air bleeds in different forms, in addition to jets controlling fuel.
Are there any moving metering needles in this carb?

Some carbs have means to adjust the timing and rate of secondary opening versus primary position.

FRM
FR Millmore

Hi again FR, yes. the metering is by way of a 'full power needle valve'. It sits in the bottom of the float chamber and when acceleration occurs the needle in the middle gets pressed down by a rod on a counter spring under vacum (this works as I have tested it)so more fuel enters a chamber helped on its way by the accelerator pump. On the DGV/ DGAV model diagram there are two pivots for the pump but on my DGEV there is only one pivot. It may well be I can adjust the action of the secondary throttle valve - will have to take off the carb again to look....have also re-checked the float level and this is per specification (41 mm plus 10 mm movement).

/Moss
Moss

Have now checked the throttle linkage and throttle valves. The second valve is supposed to be closed when idling and gradually opens to fully open when throttle linkage reaches 2/3 open on the first throttle valve. This appears to happen now. What I did find was that the throttle linkage was not opening the second valve properly and fully as the movement of the throttle cable was not fully extended when pedal fully depressed thereby not opening the second valve all the way. Have now adjusted the linkage and cable so that this happens but this has created a new problem - the engine seems 'strangled', it is not reving freely at all.
So checked the idle speed and mixture and this seems good...and the timing again, this is as it is supposed to be.

I'm stumped as to what to do next apart from going to a specialist.

/Moss
Moss

And the car now suffers from run-on when ignitions turned off and the temp-gage nearly reaches the red mark (have checked the coolant level and seems right)very quickly!!
/Moss
Moss

Moss-
Not good!
I found a diagram here:
http://www.carburetion.com/diags/3236DGVDiaginfo.asp
Is this pretty much as yours?

At the bottom is a list of the changeable parts, and there are two of everything except the pump jet. I do not know if any (or all) of these pairs can be reversed in assembly, and I do not know if the carb you have would or should have the same numbers when set up for the MGB.


One thing I see is an idle cutoff solenoid 84, which is to stop run-on.

The new problem(s) sounds more like severe timing error or total coolant circulation failure. Is the thermostat opening? Have you checked that the timing marks actually correspond to TDC? Mixed up parts or disintegration of the balancer can cause this to be wrong, and the balancer problem could be a disaster waiting.

FRM
FR Millmore

Hi FR, yes the diagram is similar but I have a diagram of the DGAV (I have the Haynes Weber Manual) and the solenoid does not appear.
Re thermostat, when I took the engine out in January I checked the thermostat by testing it in hot water and it opened at 82 deg. But of course that was then, I better check it again.
Re timing and TDC, the car starts without difficulty, I've checked with the strobe light. I did also think about a problem with the dis as the marks at 10 deg, 1000 rpm, are jumping about. In fact I would say that looking at the marks for a long time I can see a rhythm in the jumping about - what could this indicate?

/Moss
Moss

Quick stat check- start it, put your hand on the top hose.
It should suddenly get very hot when the car reaches its normal running temp, which should be stat open temp. That is normally just below or on N, but gauges vary a lot.

How much is the timing jumping about? A couple of degrees is shaft wobble, more is something else. Random sparks will really screw up the works!

Rhythm - maybe its a hiphop car!

FRM
FR Millmore

The top and bottom hose get hot. And the heater unit also gets warm which indicates to me that fluid is getting round the system as it should. I took the housing off the thermostat to check fluid level. This was to the brim.

I have a 77 USA model which means cooling system is a 'sealed' circuit with sealed raditor and expansion tank - expansion tank is at normal level, ie. 50% - am aware that fluid from expansion tank does not go back in the system and there cannot be used as a guid for fluid level. The fan is not electric but bolted to the water pump so it is on all the time. Before I started to fiddle with it running temperature was good at just below N. I have changed the fliud (50% mixture). So things should be ok but they are not ! It must be the thermostat.

Re timing marks, the jumping at 10 deg BTDC is 2 to 3 deg ie., to 12/13 deg. BTDC.

So next step:
1. Change the thermostat.
2. Sort out the dis - which will more than likely solve the carb issue. Have just reved up in neutral and it goes up to 5500 rpm. There is a flat spot at around 3500 to 4000 rpm, so ignition or petrol delivery could be a problem.

/Moss
Moss

Re thermostat - have tested it again and it works perfectly. The temperature stamp on the base of the cylinder is 88 C. So the thermostat is not the problem.
I did wonder if I had installed it the wrong way round...I pressume the cylindrical tube with the spring around it is the part which goes downwards into the body of the housing.
/Moss
Moss

"fluid from expansion tank does not go back in the system and there cannot be used as a guid for fluid level."

You can't fill the system from the expansion tank as the air won't escape, but in a working system the level of coolant in the expansion tank *is* the indicator to use. As the coolant expands with heat it pushes the excess volume into the expansion tank, and as the system cools again it sucks it back. That is part of 'burping', any air left in the system on filling from the fill point on thermostat housing or radiator is pushed into the expansion tank on expansion, but only coolant is sucked back. A couple of heat/cool cycles should be all that is necessary to expel all the air.

Doesn't your 77 model have the forward-mounted radiator? If it does then a pump-mounted fan only is totally inadequate for cooling the engine at a standstill, this is why the bottom hose is getting hot. And are you sure the fan is sucking and not blowing? A pal bought a 77 with a pump mounted fan as well as the electric, but the pump mounted fan is blowing air at the rad i.e. opposing the electric cooling fans!
PaulH Solihull

My comment was regarding when filling the system after it has been emptied (for example when I took the engine out and had to fill the system again). I must learn to be more articulate so as to minimise misunderstanding!

Re the radiator - yes, it is forward mounted.
Re sucking or blowing air - not thought about that. Have to get a piece of paper....

Still trying to get the carb to function correctly. Today have looked at everything that can be adjusted and followed the step by step guide in the Weber Manual by Haynes. Fast idle setting, secondary throttle setting, idle mixture screw setting, idle speed screw setting, throttle mechanism and the choke setting...
And now it runs worse than ever with very uneven tickover, and black smoke out the exhaust. Never had black smoke before - must be too rich. And have discoved after a proper cleaning that although technically the carb is the DGEV, as it has the electric choke, the stamp says DGAV 33B/1. In my mind this should not make any difference but when the 'numbers' do not match I'm thinking that the manufacturers have not thought things through. And what if the carb I have is a 'mix and match' cheapy - bits from different models. If this is the case no wonder I am having difficulty gettign things right.


Seriously thinking about a pair of used HI4 Su's and all the bits....

/Moss

Moss

Update: have solved the problem with acceleration; the second throttle was adjusted incorrectly (by myself). At idle it was open by 2 thousands of an inch - it should be closed. I had not seen a very small screw (about 2 mm across in the body of the carb) which adjusts the opening of this when both throttles are disengaged at idle.If this is open at idle the main circuit comes in instead of the idle circuit) The other problem was the throttle cable has not be operating properly - needed to be adjusted - it has been too short and too loose.

Regards the temperature I drained the system again, refilled and now temp shows just above N on the gauge. Still warmer that before but now not near the 'red'.

Have also managed to adjust to best lean idle but now have 'run on' when engine warm. When the idle is rich no run on, when lean I get run on. I have no anti-run on valve....

Been a very steep learning curve...which has not yet peeked!!

/Moss

Moss

Of course I mean peaked and not peeked...!
/Moss
Moss

Moss,

Regarding the run on, you might try flooring the accelerator just as you turn the key off. I suppose it's not that good to give a shut down engine extra fuel but may be better than run on.

Charley
C R Huff

Might try that. Odd to me that a lean mixture causes 'run on'. But then I have not yet fully understood what causes 'run on'. And I am supposed to have a cylinder head that runs on unleaded. Can it really be due to a lean mixture...?

/Moss
Moss

A lean mixture usually results in a hotter combustion chamber as the cooling effect of the charge is less. This will result in any hot spots being hotter, often glowing, hence the running-on which is where the mixture spontaneously combusts with compression, which is why it is also known as Dieselling. The MGB head is well known for this, at least one tuner recommends *reducing* compression ratio slightly by reducing the pier that sticks out between the valves from a point to a more rounded shape, as this is one of the causes. I have to confess I don't know why this spontaneous combustion only occurs with no ignition, one would think that the much higher increase in combustion chamber pressures as the normal progressive burn from ignition, while the piston is still getting to TDC, would cause it as well. It does of course if the timing is over-advanced but that is pinking, it's quite normal to be able to retard the ignition to control pinking, but still get Dieselling.

Run on, and pinking, with my 73 got noticeably worse with the change from leaded to unleaded. I had to retard the timing a tad from spec even with high octane (considerably more with standard grade), and fit an anti-runon valve. I tried various so called tricks, including flooring the throttle as I switched off and stalling it in 4th both of which I hated doing, I'd much rather be able to just switch off as nature intended. Incidentally retarding the timing to cope with standard octane made the engine rún noticeably hotter on the gauge, as well as making running-on worse.
PaulH Solihull

Thanks for comments. I forgot to mention, and to be honest had not considered it an issue, that I changed the spark plugs and HT leads when I was servicing the dis. I suddenly thought that perhaps that this might have something to do with the run-on and the higher running teperature. I bought them on the net - I will not mention the company but they are supposed to be high performance etc, and for the record I have not at any time expected any more performance whatsoever. The colour looked good...yes yes I know, very dandy of me!!

Perhaps the temperature created by these new plugs and leads is too hot. I'll put the old leads and plugs on to test.
Moss

As Paul mentioned, run on is quite common with B heads. When I set up my head for performance application, I removed the small protuberance at the center of the combustion chamber that is supposed to be the main cause of running on. It made very little difference. For the last 30 years, I've gotten used to shutting down the engine, in first gear, while letting out the clutch. It's become second nature. I'm running a Kent 285 cam that requires a slightly higher idle speed that doesn't help the situation. Having had the head converted to unleaded specifications will have very little effect in curing running on. Getting your engine to idle at the lowest possible speed is usually the best way to cure the problem. RAY
rjm RAY

Hi Ray, thanks for your comments as well. I've actually reduce the idle to as low as possible already - 650 rpm. I must be doing something right as the engine ticks over very well compared to before I did the service on the dis and at the usual 800 rpm. The norm for the engine I have is 800 rpm. It has taken me alot of time with the dis service and trying to understand the Weber but the engine is running much better than before...a very good feeling!

I researched the price of a pair of good used HI4 SU's with all the bits....I'll be waiting a while I think.

I'll carry out the test with the old leads and plugs tomorrow...

/Moss
Moss

If you bought some "sucker plugs", they could be a problem, and if they are too hot range they could be engine killers. Quit being cute and tell us what you did!
Leads shouldn't affect it.
There is some problem if it will not shut off at 650rpm; I've never had one that dieseled below 900.
A possibility is that it is just carboned up from all the fiddling at rich running conditions, so I wouldn't worry about it until you can drive it briskly for a hundred miles or so - often cures this sort of trouble.
Old trick is to hold the engine at 4000rpm and spray mist water down the carbs, which cleans out the carbon, though it is better to do it under load, which takes some engineering.

Paul-
"Incidentally retarding the timing to cope with standard octane made the engine run noticeably hotter on the gauge, as well as making running-on worse"
Seems to me a clear case of needing to recurve the distributor. "Pinking" should only be a problem around max volumetric efficiency, around 3000rpm WOT for stockish engines, requiring retard. But retarding it otherwise to accomplish this is bad, so you need a flatter curve.
What is the base timing you arrived at, static and idle? Too much retard causes the exhaust valves to run hot, really increases the diesel problem!

FRM
FR Millmore

FRM - I'm sure it does need recurving, along with pretty-well every MGB and related era car in the universe given the age of engines, distributors, and the very different fuels we have compared to the 60s and 70s! It's just not worth the time and effort on a rolling road to determine the ideal curve and to try to achieve it for a road car, which in any case is going to be much harder with a vacuum advance distributor, and I've no interest in fitting a 'performance' (for which read poor touring economy) distributor. Anything else is just poke and hope and every engine is different to a greater or lesser degree. I *have* poked and hoped to some degree, replacing the springs (which are available for named 25D4 distributors from Distributor Doctor) and substituting a vacuum capsule with more advance then retarding the timing a little, which did improve things. Other than that I just use the highest octane I can get, and set the timing just short of pinking at any combination of throttle, revs and load (high compression engine). That, together with the anti-runon valve, and everything is hunky-dory.
PaulH Solihull

This thread was discussed between 02/04/2012 and 07/06/2012

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