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MG MGB Technical - emissions controls gone
|our '70 mgb came to us with an engine different than the original, along with the swap they took off the emissions controls. we had the carbs rebuilt, new plug wires rotor cap, etc. done. anyone have any input as to how we can remedy(inexpensively) or cicumvent the emissions controls problem? |
thanks in advance
|Problem? What problem? Do you need to pass a local inspection, or are just trying to get the car back to original?|
|Removing the emission controls will not cause any problems and will restore some lost power. Just be sure all possible vacuum leaks are sealed, especially the air rail plug holes in the head. You will probably have to check and adjust the timing. If you need the controls for emission inspection that's a different story.|
|the problem seems to be a rough idle, something about the crankcase venting in to the intake? i need not meet any emmissions testing but would like to find a remedy for the rough idle. is there a key component missing from the crankcase vent tube?|
|sorry, there is a bit of fuel getting in to the oil. also is it nessesary for the air filters to have warm air induction? the original filters are long gone and replaced by foam filters. |
|thx lewis will check the rail, is it possible that what i see is a pvc on the rail?|
|>Removing the emission controls will not cause any problems and will restore some lost power. Just be sure all possible vacuum leaks are sealed, especially the air rail plug holes in the head.|
Not really. In fact, improperly removing emissions controls can make the car run worse. And leaking air rail fittings would not cause a vacuum leak -- they're on the exhaust side and if anything would be an exhaust leak!
The only emissions control on a 1970 B that can reduce power would be the air pump -- it pumps fresh air into the exhaust stream (after the exhaust has left the combustion chamber) and there's a slight parasitic drag in turning the thing, but it's nothing you can feel in the driver's seat. I know this from experience.
The other devices on the car would be:
Gulp valve: opens at overrun (i.e. when the throttle is closed) to prevent the mixture from going excessively rich. It's closed and thus doing absolutely nothing at steady state throttle and under acceleration, so it cannot reduce power.
Evaporative emissions system: Recycles gasoline vapor and returns it to the fuel tank. It's also part of the crankcase breather system and it's operation is calculated into the idle mixture. It has absolutely no effect on power and does a good job of reducing the amount of unburned hydrocarbon the car releases. It's effect on mixture is so small it's completely masked when you're driving, but if you set the idle mixture after having removed it, you're likely to be off whilst driving. IOW, the car runs worse, not better.
Your best bet would be to study how the systems work and make sure that everything is in good repair and properly tuned.
I may be misreading your posts, but you sound as though you're somewhat inexperienced with these cars. If you can, find and join a local MG club and hook up with someone who really knows the cars and will help you learn about them.
For your rough idle, I'd start by checking for vacuum leaks around the throttle shafts, the base of the carbs, and all the various hoses. If there are leaks, they need to be fixed. Then, set the valve clearances, check and set the points, inspect the cap, rotor, and wires, check and set the plugs, set the timing, then adjust the carbs -- in that order! The carbs must be last. Once you've got everything to a known, proper baseline, you can then start your diagnosis if the problem remains.
|John. As Rob noted, the air pump is the only real emissions control on the car. There should also be a line from the front tappet chest to the carbs, with a Y fitting allowing the three points to be joined together. If not, there should be a "mushroom" valve on the top of the intake manifold with tappet cover joined to it. If the mushroom valve is bad, it can cause excessive oil consumption and the engine will not run as well as it should.|
Check the ignition, set the timing, adjust the valves, then, check the carbs. Excess fuel into the oil is not a good thing and is commonly caused by an excessive mixture.
Check that, when the choke is in the off position, the jets rise back up into the carbs correctly. They should only be about .055" below the "bridge" of the carb. Several of us have had a problem with the jets not returning properly, the mixture being too rich, and poor running as the result. If new spark plugs immediately cure the problem and the old ones look sooted up, the choke might be the first thing to look at.
You might want get a copy of Porter's mgb restoration Manual (available at Amazon):
It has a section on removing the emmisions control equipment that might help you sort out what was done, what should have been done, and what shouldn't have been done.
|i am beginning to see light at the end of the tunnel, i think. :)) the air pump and all emissions parts are gone, as is the gulp valve and any hose from the tappet cover to the carbs.the breather tube on the tappet cover instead has a filter there. there is a hose connecting the crankcase to the carbs, when it is connected it runs very rough. it smoothes up a bit while disconnected, and the vapors smell of fuel.|
the old plugs were in fact sooted up and the intake was carboned as well. my mechanic replaced the plugs, points, condensor rotor, plug wires, and set the time, we had the carbs rebuilt.however the valves were not adjusted, this will be done next, then we will try tuning the carbs again, after checking the point gap and time.
on the inlet manifold there is what appears to be, a pcv valve in one of the topside holes, should this be correct, is this the point at which the tappet chest vent should be connected to, with a y fitting for the carbs as well? if so then where does the line from the crankcase connect to, or should it be connected to the same line as the tappet and inlet maniold then to the carbs.
in any event i will aquire a copy of the book you mentioned and follow robs' advice, checking the choke as well.
thak s again for all the input, it is much appreciated.
|John. The line from the carbs should be attached to the front tappet cover. This supplies a slight negative pressure to the engine. There should be no PCV valve on the intake manifold if the tappet cover is vented to the carbs. There should be no vent on the body of the valve cover. This was used on the later cars to connect to the charcoal cannister which came in about 72. Rather, the valve cover vents through the cap. |
It sounds like there have been some changes made to your car over the years. In light of this I would recommend you start with the following set up and proceed from there:
Plug the intake manifold where the current PCV valve is after removing the PCV valve.
Run the line from the front tappet cover to the carbs using a Y connector.
Put an air filter on the elbow of the valve cover to provide clean, filtered air intake for the engine.
This should get you started and allow you to begin to trouble shoot the problems in an effective manner.
| Thx Les, yes Rob I am a newbie to the mechanics of this fine touring machine, and when it comes to emissions and the carbs, I am really at a loss. |
It would seem that everything is connected the way you suggest, Les. Except for what i believe is a pcv valve, on the inlet manifold.
I wasn't sure about the tappet chest cover, but after research I realized this is what i meant by crankcase. Sorry for the confusion.
The motor is from a later production, I know for sure,( the car is not at hand to check the block number, still in the shop). But, for sure the valve cover has a vent tube.
In addition to the engine swap they either replaced the tranny with a standard 4 spd, or else the O/D is not functioning. I prefer not to drive at the higher RPM so am going to look into it.
John, I ordered the manual you mentioned, should be here next week. Thx.
|With all due respect Les, I must diasgree. 1970 had evaporative emissions and the vent tube on the valve cover; it was the first year so equipped. My '69 has the vented cap and no vent tube. You're correct that there should not be a PCV valve. I think what JC is seeing is the gulp valve.|
JC, I've put a photo of my 1970's engine with the systems labeled -- except the air pump, which the PO removed. Hope this helps!
| Thx for the pic Rob. |
Your '69 engine looks like ours. Our block number
starts with 18HGV, or 18HV, I am sure of the V . Its
hard to get specific when the car is still
The gulp is completely gone on ours, If i knew how
to send you the pic back, or up-load it i have
circled the spot where the valve is. In your pic it
is where the redish colored adapter is, on the
manifold side of the gulp.
You can send the picture to my email address listed (deleting the
If there's a V in your engine number, it should just be 18V...... A 1970 engine would be 18GK, I think. the photo I posted is a 1970. My 1969 is a 18GH. It has basically the same emissions control, but as Les mentioned, without the evaporative controls and a vented oil filler cap rather than the tube on the valve cover....
Looking at the Moss site, it looks like the PCV valve wasn't used after 1968. It sounds like you've got a mix of components.
|jc, if its any help, my car always ran worse with the vent tube attached to the carbs. I also run a small filter on the tappet cover and plug the ports on the carbs. My valve cover has a breather hole in the oil cap - the two vents seem to work appropriately. |
It is very common in these cars to have problems inside the distributor. Besides bad points, condenser, cap, and rotor, the vacuum advance canister, advance weights, and springs can all be problematic. A thorogh cleaning and inspection may be in order as well.
Fuel in the oil should be dealt with immediately. It was probably caused by bad ignition components and possibly the carbs. It sounds like you'll have it running great in no time!
|Rob. I bow to your superior knowledge. I had thought the change had taken place in 71, but the illustration in Moss' catalog shows that 70 was the beginning.|
So, I would agree that the valve on the intake manifold is, probably, the gulp valve and it should be removed and the opening plugged.
The tappet cover vents to the carbs and the rocker arm cover should be either attached to a charcoal cannister (recommended) or have a filter attached.
This brings up another area--vent line from the fuel tank. The tank should have a vapor seperater in the trunk with a vent line going forwards to the charcoal cannister. If there is no charcoal cannister, where is the line venting to? This might be part of the problem.
Charcoal cannisters are available, used and new, and are an excellent idea. They keep down the fumes vented to the atmosphere and do not, in any way, affect the running of the car. An old one can be rebuilt and there was much discussion on how people were doing it about five years ago. Should all be in the archives and available for study.
Check for a line going to a vapor seperater in the trunk on the right hand side as you are facing forwards, then, see if the line is going forwards into the engine compartment (steel line comes up on the right side of the firewall near the box which holds/held the charcoal cannister. I have seen these lines disconnected, in the trunk, filling the trunk with vapors. I have also seen the line going forwards and needing to be replaced if the fuel system was to work properly. (Bear of a job to replace.) The line from the trunk goes into a connection, near the right, rear wheel, with the hard line running under the car, forwards, to the cannister.
A lot to check out to see what the problem(s) may be.
While you are at it, check the plugs on the ends of the intake manifold to make sure they are in there securely. They have been known to come loose and this can make troubleshooting difficult.
| Les,good idea to check the vapor seperator.It was hooked up backwards and filling up with fuel, causing it to leak fuel into the trunk. I am not sure where the line from the engine compartment the the seperator is connected, since the cannister is gone also. I will check on that Monday when the shop opens. |
|Jeff. For some reason, last time I hit the "thread" button, you reponse did not pop up. Since you posted a hour before I did, it should of. But, I have seen this happen before.|
In answer to your post, I have no experience running the car with the tappet cover connected to the carbs. Friends who do have similar systems have not reported problems. But, when we get familiar with our own cars, we do not tend to notice some of the problems, thinking that they are operating correctly. My daughter's car once had a dead cylinder (cracked exhaust valve which did not back fire through the exhaust system on the firing stroke) which she did not notice, but I did, immediately, when I took it out for a drive. So, you may well be correct.
If that is the case, I do have a very good idea of the performance on my 68GT with the "mushroom" valve from the tappet cover to the intake manifold. It runs quite well with this set up and will meet the Arizona required emissions testing standards with no problems.
Thus, John may select to run the tappet cover vent to a mushroom valve (available from Moss Motors--see the 68-69 emissions equipment diagram) and simply bridge the two carbs with a piece of rubber hose. (I had to replace my carbs for emissions testing and the only ones immediately available were the later type with the connections for the hoses. We simply ran a piece of hose between the two carbs, the car passed emissions and has continued to run well since. Hopefully, this winter I will have time to replace the newer carbs with the "new" set of SU carbs for the 68 which had lasted for three years before developing problems.)
John, A charcoal cannister is an excellent idea and you need to find out how the gas tank is vented. It may be that the later model filler neck was replaced with an earlier model filler neck and a vented gas cap. If so, the hole for the vent line, at the tank, should have been capped off. The earlier style tank used a vented cap, having something looking like a single bladed propeller, which locked onto the filler neck. The Rubber Bumper cars had a different filler neck which had a cap with two teats on the outer edge which fit over two cut out on the outer edge of the filler neck. This gas cap was non-vented and made a tight seal with the filler neck.
Perhaps Rob may be able to tell us, exactly, what proper gas cap and filler neck for the 1970 model was and help you to determine what you have.
In any event, I have a website, www.custompistols.com/ which provides some information on dealing with MG related problems. It also has a much better server than the one I list for this site. If you should need a charcoal cannister to add to your car, please e-mail me through the website and give me your mailing address. I have a spare which you may have should you need it.
I got the photo. The bit you circled would have the mushroom-shaped PCV on an earlier car, but on your car it should have the gulp valve as shown in the photo. The tappet breather should be connected to the carbs as shown in the photo as well -- it's the same setup as on my '69 and on that car works quite well, so I assume it should function equally well on your '70.
My '70 is stored off-site, but I need to pull some parts from it, so I'll try to get a few photos of the filler and cap for you. I don't have any photos of it at the moment.
Les, I thanks for the complement, but I can't claim superior knowledge! ;-) I can only claim the dumb luck of happening to have a '70 parts car from which I can make observations.... :-)
| Today is the day, I present all this wealth of knowledge to my mechanic. |
I will be gone for most of the week and wont be able to inform you all of the outcome until the week-end.
Les, I'm sure it has the original fuel tank. I had to remove it and flush it. the cap is a vented cap with the blade as you described.
I believe the line to the vapor seperator is connected to the carbs at the moment, but cant be sure until i go to the shop.
I also believe the engine is a 72-74 model, the valve cover is black, the earlier 70-72 were moron, according to another source.
I leave for Kentucky today, to earn my keep so to speak. Hope you all have a good week, and will talk to you when I return.
|Just to confuse matters more, there are two different 1970 MGB emissions setups. 70 was the first year for the evaporative control, but not all had this. There are in fact one with the evap control (CA model 18GJ engine) and one with out (Federal model 18GH engine) The other emisssions setups are the same. The big clue to this without the original engine would be the gas tank. The CA model is non vented with the return line on the filler neck in the trunk along with an expansion tank. The Federal model is vented with no return line or expansion tank present. Even though I'm in CA my 70 is a federal model. This is noted by Clausager. JC, there should be a line from the front tappet cover fitted to a Y with tubes running to both carbs they will have a fitting present for these tubes if they are the 70 type carbs. Look for a little tab on the float bowls correct carbs are AUD405 series. |
|JC- I believe I still have the smog spaghetti/pump/etc., eng GHN with charcoal cans, originbally fitted to my beloved 1971 splittail when I bought it new off the showroom floor in Sept 1970. Contact me offline. In Calif., I no longer have to meet smog, and have it registered as a "Classic". Curiously, with a fully hot-rodded, crossflow,1 3/4 SU, Hans 2.5 jet-hot coated header, Peco, engine, I still beat the old smog req numbers due I believe to the efficiency increase! AND That's without the manifold/pump/etc.!!!! Anyway I'll make you the sweet deal if you want it. Ron- Thx for your contribution. After reading above, I was getting concerned re my engine numbers and production Date.Vic|
|Ron, I pulled my paperwork and my BGT has an 18GJ engine. It'd be interesting to find out how a CA-spec car ended up in NC!|
|69 to 70 was an interesting period, lots of changes. How a federal spec B wound up in CA? For the most part rust free as well. Mine is just about dead bone stock, and does have the vent tube at the back of the valve cover, but it is capped with a rubber cap and a two wire clamp. I always thought this was a quick fix, but is in fact stock. Also has a vented oil filler cap. It also has the original (or a matching primrose) aluminum hood to boot. I can provide pictures of the stock emissions if needed.|
|Ron and Rob. Since you two seem to be the default "experts", actually having access to examples of this model year, please take a look at the following areas:|
Gas cap and filler neck.
My 68, with a vented cap, has the "propeller" style latching mechanism inside the cap which fits into the two cut-outs on the inside of the filler neck. The RB cars had a different style cap, but they were also equipped with a different filler neck having the flap for rollover protection and the restrictor to take the smaller, unleaded gas, filler nozzle. I had a 73 parts car and remember the filler neck being visibly different that the filler neck on the 68.
Can you describe the type of gas cap latching mechanism on your two cars and describe the shape and length of the filler neck? This may be useful information to have available in the future.
It would be worthwhile to know whether both cars had the provision, near the filler opening, to attach the vapor line/vent. Since about one half of the cars imported were to California spec, I wonder if they simply used the same gas tanks with both models, capped off the opening for the vent line and used different filler necks/gas caps during this period. Closed system fuel tanks/carbs should have been part of the EPA /DOT plan for the following year and it might have made good sense to change over all of the cars and standardize on one fuel tank for that year and later years.
I would be interested to know what you discover. Thanks, Les
As I recall (will look when I get home) The B has the propeller style vented cap. Twist on two tabs 180 degrees apart. The filler neck is full diameter no restrictor. Angled fill tube attatched via rubber hose to tank, no vent/overflow tube. Full 12 gallon capacity with a single outlet BSP fitting for the fuel line to the fuel pump.
| I misspelled maroon, in my post about the color of the valve covers,70-72. Sorry. I must have been distracted. Primrose may be even more correct. |
Hmmmm, where to start sorting?
Ron, our Roadie has the vapor seperator located in the trunk, so it appears this would have been a CA spec model.
Instead of the return line, (absorption cannister to vapor seperator)coming off the absorption cannister, which is long gone or never was , it has been spliced in to the carb to carb line.... which should have, I believe, gone in to the absorption cannister, then to the vapor seperator. Could this be the main problem? If so what is the cure? Go back to a complete emmisions system or??????
The carbs are in fact fitted with tappet vent connectors, no tabs present though. That part of the set-up appears to be correct.
An air leak check turned up negative, new points, condensor, rotor cap plugs and wires, and valves were set.
I'll post the engine number next week, as soon as I can get access to the shop. Though i am most sure it is an 18 V series.
I'm anxious to speak with my mechanic after my absence. Maybe he has the problem solved by now.
|still no luck, seems that there is to much fuel getting to the carbs.|
|JC, A vapor separator should have been on 50 state MGB's as Rob mentioned. Your comment about the vapor separator "It was hooked up backwards and filling up with fuel, causing it to leak fuel into the trunk." I don't understand why hooking it backwards would cause it to leak into the trunk/boot. There should be two fuel lines hooked to it. one goes to a fitting on the gas tank, the other goes to a fitting in the corner of the trunk floor. Unless the lines were leaking any fuel in the separator should have leaked out through the fitting in the trunk floor on the ground or in the line to the original emissions cannister. |
Starting at the fuel tank you need the following for the system to work. http://www.mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=29001
The fuel tank must be vented. If you still have the original components your gas filler tube item # in the above link should have external gas cap lugs. Your gas cap should be non vented. The gas tank is vented through the vapor separator and it's associated hoses. see items #77,76,81,83,85,86 & 71 in the above link. #71 was connected to the cannister. Without the cannister you can vent the fuel tank through the under car lines from the trunk floor to cannister. It would be a good idea to have a simple filter to prevent getting clogged. That should take care of fuel tank venting.
You mentioned the carb to carb line shown passing above the air cleaners in the above link, (carb to carb line isn't numbered) is connected to the going to the cannister/vapor separator. The carb to carb line is for carburetor venting and originally was attached to the top of the cannister. Venting was through the emissions cannister through #65, cannister breather tube. If these two venting systems are tied together, the fuel tank and carburetor systems aren't working as they should. With no emissions cannister you can vent the carbs through the T connector and a length of fuel hose to provide carburetor venting. In any case the two venting systems, fuel tank and carburetors should have independent venting to function properly. It that doesn't solve the too much fuel problem the carburetors need to be looked at again to determine why.
The crankcase venting has already been discussed. I would remove the old PVC valve and plug the hole. That assumes the venting is tied into the carburetors from the y connector to the front tappet cover. I used a rubber stopper to plug mine, I know someone will laugh but it's been there seven years and never blown out or leaked.
|I was under the impression that *all* North American tanks with a tank vent and a non-vented fuel filler cap had the tank connected to the charcoal canister, via one of two types of seperator/expansion tank, none of them vented on to the floor. Later fuel pump vents were connected to a chassis rail nipple and thence to atmosphere, but this is nothing to do with emissions, just pressure equalisation, and applied to all cars - emissions and non-emissions. Non-emissions *carbs* vent onto the floor, but again emissions carbs vent via the canister. As long as there *is* a vent to atmosphere both tank and carbs can be teed together and share it, that is what the charcoal canister did. |
However I recently helped someone sort out a poor running problem that eventually turned out to be the carb vents and the tank vent had been connected together, *without* a vent to atmosphere. The effect of this was that as soon as any fuel was used from the tank it applied a slight vacuum to the carb vents, which sucked the fuel from the jets, i.e. exactly how the anti-runon valve does its job!
|Paul Hunt 2|
|Paul, Your assumption is correct, the tank was connected through a vapor separator to the charcoal canister. In my post I said, "The gas tank is vented through the vapor separator and it's associated hoses. see items #77,76,81,83,85,86 & 71 in the above link. #71 was connected to the cannister". If I understand JC's last post I believe his fuel tank vent line is connected to the carburetor vent lines, probably where the canister was located. In one of JC's posts he mentioned that the vapor separator hoses were connected backwards causing a fuel leak in the trunk/boot. |
I attempted to say that each system can be vented separately with the existing lines and hoses, a charcoal canister isn't necessary but the two systems should not be tied together.
| Paul, maybe you hit it. Pressure equalization may in fact be the prob.. Will try checking the chassis rail nipple, if it has one. The PO had sprayed an undercoating on the car, maybe plugging the vent in the process. |
The only vent to atmosphere i can see on the car is a vented gas cap. the PO drilled a hole in it for venting purposes.
It makes sense about the vacuum created by having everything( carb vents, vapor seperator, fuel tank)connected. As Clifton suggested, the two must be seperate.
How did you resolve the issue?
A pressure check of the fuel pump yielded 4 psi. From a source in Denver( the person who rebuilt the carbs) it could be to high for this altitude,( ~ 4,000' above sea level).So the mechanic wants to try a pressure regulator first then recheck the carbs.
I am still with the idea that it is a venting problem more than fuel pressure.
I can not see anywhere that a charcoal cannister was ever mounted on the firewall, by the heater core. No holes or bolts, nothing to indicate there ever was one.
|Clifton, where would i run the vapor seperator line to, instead of the carb to carb vent line?|
|JC, You don't need to connect it, leave it open. The main thing you need to do is get the carburetors vented since the tank is now vented through the gas cap. Just separate the two lines where they are connected and leave them both open to atmosphere, that's the easy way. I would tie some foam or something for a filter over the ends. As Paul said they can be tied together but you would need to install a vent to atmosphere somewhere in the line. |
I didn't get both links added to my above post, thought I did.
In the emissions plate in the above link the canister #68 sits on the flat area where the brake and clutch cylinders are located in a Right Hand Drive cars. The canister bracket has four mounting holes. The front two uses the existing blanking plate rear bolts for mounting. You should have two welded nuts behind the blanking plate for the the rear canister bracket mounting holes.
|Clifton - it was the "through the fitting in the trunk floor on the ground" bit that confused me.|
JC - if your fuel filler cap is vented than that should be enough to vent vent the tank at least, and the carbs also unless the pipe between carbs and tank gets blocked and there is no other vent for the carbs. Originally it would have been a non-vented filler cap, of course, with both tank and carbs venting through the charcoal canister to atmosphere, the canister acting as a fume trap and filter. In normal driving there is a third connection to the top of the canister that goes to the rocker cover and the crankcase ventilation. The continual flow of air through here purges the canister of fumes, burns any fumes from expansion in tank or carbs, as well as purging the crankcase. For this reason a non-vented oil filler cap must also be fitted.
|Paul Hunt 2|
| matters would be a lot simpler had the original motor been left in.|
engine number on this one is
18v 584Z L2912. Car manufaction date is 11/69, could i have a 70,s model without the cannister? If so i should be looking at the 69 model emmissions plate from Moss.
I havent heard from my mechanic as of yet.
Still hoping here.
A big thanks to all of you.
| An after thought, could a semi loose carb to card throttle shaft be at fault? I would have thought the rebuider would have replaced it but, no.|
thx. agn. jc
|JC, If your car came from the factory with a vapor separator installed I think it would have also had the emissions canister and a non vented gas cap.|
If I understand your question, the linkage between the two carburetors should be loose. During carburetor synchronization the levers on the shaft should be adjusted so both carburetor throttle shafts open at the same time.
|Clifton, the part i am referring to is the connecting rod on the front carb. pn 37685 in the Moss catalog, http://www.mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=28995#56.|
|Jc, You left out a numeral, Moss parts have 6 numerals. The closest number I see is for for item 56, Rod Connecting, Moss # 370-865. That should be the rod for connecting the chokes. The throttle lever and spindle isn't shown in the Moss catalog. I'm going by photos and drawings plus a little memory from the past as I have HIF carbs and don't have a set of HS-4 carbs to look at. The rod and the throttle lever have levers and pins on each end to engage the choke and the throttle levers/arms for each carburetor. The levers and pins on the shafts have pinch bolts for adjustment during carburetor synchronization. Some looseness is normal for both and does not indicate wear. What is important is that the respective arms and pins be adjusted during carburetor synchronization to open both carburetor chokes and/or throttles at the same time. The synchronization procedure specifies a little play in these components, otherwise there can be a change in idle speed when the engine warms up and parts expand. The area that should have little or no looseness is the throttle shafts, Moss item #40 . If they are loose/worn it may be difficult to get a decent engine idle. Throttle shaft wear will not have a great effect on speeds above idle.|
Look at this photo in the Chicagoland MG website;
You should be able to see the choke rod and the throttle lever & spindle. You can also see the levers with the pinch bolts.
If this doesn't answer your question let us know.
|I had a look at the '70 BGT last night -- the fuel filler cap has the internal ears (i.e. on the outer edge of the cap, pointing inward) and the filler neck has the notches on the outside edge of the neck.|
|Yes that is the later style for the emissions models. My Federal spec Non evaporative control model has the tabs on the inside section of the gas cap pointing outwards, and the notches on the filler neck are inside the neck itself. Just took the B for spin, wonder how much longer the 8 year old battery is going to last.. |
| The car has been at the shop for to long now, i am getting a little worried if the problem will be found there.|
That is a good pic Clifton. Though the rod I am refering to isn't visible from that angle. It is the one on the front side of the front carb, closest to the manifold, a bronze or brass looking metal. On the manifold side of the bowl. Maybe like you say it has little effect should it be loose.
The last time i drove the car it ran fine till I came to a stop. Then it died, flooded right out, and almost refused to start. But the bucking on acceleration was gone. So i returned to the shop, the mech adjusted the carbs a bit and I set off on another test drive. This time there was backfiring and a little missing going on.
So back to the shop I go, hi ho.
Thats where it is now.
Rob your 70 BGT cap and filler neck is the same as ours. Sorry about the confusion earlier.
|Jc, I believe that would be the throttle shaft, item 40 in the Moss carburetor plate. Yes, it could cause idle speed problems, the mechanic that rebuilt your carb should have repaired it or mentioned the problem to you so you could make a decision about what to do.|
| Clifton, thx. for the link http://www.chicagolandmgclub.com . There is an interesting article there, about pressure regulaters. The author sets the pressure at 1.5 psi, where our electric pump is producing ~4 psi. The mech. is in the process of installing one for us. Hoping this will lean out the carbs. |
There's also an interesting article about re-bushing the throttle shaft, should I need to repair/replace the throttle shaft. Unfortunately for us the carb. rebuild was done in Denver, ~130 miles from us. Yes he should have dealt with the shaft at the time, now we will need to completely dismantle the carbs to remedy the loose shaft and re-bush the shaft.
I think in the future i will not rely on any mechanics, though our local guy is really good. He has always done a superb job for us on our other vehicles, and is very knowledgable. His knowledge of the MGB is limited, but still has the advantage over me, by his 30 yrs experience with all vehicles.
|Jc, 4 psi may be a little high but if you have a SU fuel pump it should be OK. I didn't have good luck with a regulator set at 1.5 psi on my car, in fact it stopped running. 2.5 psi worked OK but I have removed the regulator. My fuel pump is not SU but it's maximum output is supposed to be 4 psi. |
| Clifton, I'm not sure if it is an SU pump. I can check this week sometime.|
I would wonder if the needles were sticking, but since the carbs were just rebuilt I think I can eliminate that.
Maybe I should install the charcoal cannister again. At least then it would be earth friendly, even if it doesnt correct the problem.
|You cannot eliminate something that has just been rebuilt, with twin SUs the same error could have been made on both carbs. A fuel regulator won't lean out the mixture. It maintains a constant *pressure* (as much as the fuel pump allows it to) on the input side of the float valves. As the float valves open the pressure will drop and so the regulator will compensate by increasing the flow to maintain the set pressure. Only if the regulator somehow *restricted flow* as well as regulating pressure could it weaken the mixture, and that would only result in correct mixture at one throttle opening. Less that that it would be rich, more than that it would be weak. If it were correct at idle then the restriction in flow would mean that it wouldn't accelerate at all.|
|Paul Hunt 2|
| it could be possible the wrong size needles and seats were used, i would hope the rebuild guy woud know what type of kit to use, i dont thinl he used the master kit because the throttle rod wasn't replaced. hmmm , een possibly the flaoats are not adjuste correct. |
the specs i have seen say 4 psi.
anyway i just got home from a trip again,
thanks for bearing with me. if i learn anything i will try to relate it to you all.
This thread was discussed between 12/11/2005 and 30/11/2005
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