MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - Why will my be not start

I will tell you what I have tried starter fluid, oil in the spark plug holes, new plugs, starter, cleaned out the carb, fuel pump works, readjusted the carb (to factory settings). Not sure what to do with the car.

Car information.

1977 MGB (questionable condition)
1.8L engine
45 series side draft carb
Long tube header
Otherwise stock.

Confused MG owner

Confused. Much will depend on where you live. The Weber 45 DCOE carb is often used on highly modified engines. It may not be the best choice for an "Otherwise stock" engine, at least according to the tests I have seen and the experience I have had. In this case, I would prefer to take the car to a competent professional, preferably one with experience with that carb, and let the mechanic get the car running.

One thing you can do is have an assistant turn the engine over while you use a timing light to observe when the spark is occuring. Static timing, with an older distributor, is not all that accurate and, often, the use of an assistant and a timing light can get a car started when trying to do it by yourself will not. But, with the DCOE, a very complex carb, a professional set up would be the best recommendation. Les
Les Bengtson

I have a 45DCOE on my own car - but my engine is
not exactly stock.

In my opinion, the 45DCOE is a bit too much carb
for a stock B engine - even when it's choked way
down to 36mm. I often wondered whether if a
40DCOE would be better suited for a street, or
mildly tuned, application.

Des Hamill's "How To Tune Webers and Dellorto
Carbs" is an excellent book to get your feet wet
on Weber carbs stuff.

If you happen to have a good set of twin SU's laying about - I'd seriously consider bolting them on,
however.

Anyway...I think we need more info from you.

Does the engine just spin and spin from the starter
without any other sign of life whatsoever?

If so, then it's my initial impression that something
is goofed in the Ignition Department.

The clue: You should've gotten some sort of sign of life when you used the starting fluid. Anything.
A backfire. Spitback from the carb throats.
Popping. A burst of life, then sudden death, etc.

In anycase...from now on...lay off the starter fluid.
You don't need it, and it can wash the protective
film of oil from the cylinder walls and piston rings.
The DCOE Weber has pump jets that squirt a
stream of fuel down each throat whenever the
throttle is opened or "blipped". To check this - with
the engine off, use a flashlight and look down each
carb throat and open the throttle. You should see
(and hear) the pump jets squirting a stream of fuel
down each carb throat each time you do this. You
should be able to smell the raw fumes from the
fuel after this, too.

The plugs may be new...but are the plugs actually
firing? Are they wet and smell of raw fuel when
pulled out from the engine?

Is the ignition timing correct? DCOE Webers tend
to like a little bit more initial advance, but you'll have
to experiment back & forth to find your particular
"sweet spot" for this.

On cars with DCOE carbs, the distributor should
be converted to full mechanical advance and
re-curved - and the vacuum advance deleted.
Having just said that, you should still be able
to bring the car to life with a stock distributor,
nonetheless (- but you will not be taking best
advantage of having a Weber DCOE until the
distributor has been converted, tweeked and
massaged).

What do you mean by: "readjusted the carb (to
factory settings)" ? The Weber Carb Factory?
...or the BMC Special Tuning specs? Either of
these specs are wrong for a stock B engine.
What, exactly, are all the jet and choke, and
secondary choke sizes on your carb?

Even if the carb jets are not correct, you should still
be able get a couple of cylinders to fire and spit at
you in anger.
Daniel Wong

Meaning by factory settings I found a website that deals with Webbers and they had a factory tuning pdf file for all of the Weber carb set-ups. I down loaded it and did what it stated were the factory settings for the screws on the carb for the butterflies turn things. It stated that it was a base line that should allow the engine to run then fine tuning would be need to make the engine run its best. The car has sometimes in the past acted as if it would turn over however no life in the engine. The engine has back fired through the carb and started a little fire. Then engine did run for a few seconds once before I cleaned up the carb, however when I let off of the gas the car died and has never come close again. Timing has not been messed with since that time. A have the stock distributor and like the carb I have no other so they will have to work for now. No one in my area that I have tried even knows what a Weber carb is. Let me know what you think I need to do to get this thing running.
Confused MG Owner

Did you check our the fuel pump?? Does it make the "clicking" sound?? These are very finicky and sometimes do not work. Points get fouled...sometimes a good "bang" on it will bring it back to life. Check the "archives".

Ocassionally I have to prime mine directly into the hose leading into the carb. Also..have put some into the fuel filter.

Also...did you get the spark plug wires back in the right order. (1342 - with the back plug as #1) I had mine off over the weekend cleaning the plugs..and got them on wrong..and was spuddering...and backfired with air filter assembly off.

I think more info is needed....

Ron
'79B
Ron Eberhart

Confused. Danny is one of the few people running the DCOE and is highly regarded for the quality of his advice. Might I suggest that you list, exactly, how your carb is set up? Include not only the idle mixture screw settings, but what jets are being used, etc. Then, people who are running DCOE carbs can know how what they are running compares to what you have.

One word of caution, unless the Weber settings you down loaded are specifically for the MGB stock engine, they may be of no use to you. These carbs are made to be used with a wide variety of engines and, due to that, may be set up in many different ways. You need to know what you have in there before someone can tell you if the carbs are even capable of functioning with your engine. Les
Les Bengtson

Setting up a Weber carb takes a lot more than simply turning a couple of screws.

You have to ascertain the sizes of the idle jets,
main jets, air correctors, emulsion tubes, choke,
secondary choke, etc. that are now on the carb
...and then you have to get a hold of, and install,
the correct sized parts that are recommended for
the state of your engine setup. This is only as a
baseline for further tuning. Expect to have to change the jets again, later, after you get the
car idling and running.

The float level has to be checked and adjusted,
if necessary.

After you get the car idling and running - it'll take
a bit of "seat of your pants" road testing to fine
tune the jet sizes on your carb, until you finally
settle on a set of jets that feels right to you.

I would also re-check the ignition timing, just to
be sure that it's correct. Try 15 degrees BTDC
to begin with.

The only adjustment screws on the carb are the
two idle mixture adjustment screws, and the one idle speed adjustment screw. Fiddling with these
screws will do little to help you if the jets and
chokes are not first correctly sized and the float
level set correctly.
Daniel Wong

Danny. I knew it was a very complex set up to provide maximum performance out of the DCOE series. That is why most of us use the SU or Weber DGV with our relatively standard cars. Would you be willing to write some of these things up. There is room for another tech article on your portion of the website. A lot of people, like me, do not fully understand the Weber DCOE series and when it is most applicable. Peter Burgess mentions it in passing on the "big bore" engines. If you have the time to put you thoughts in order, then will send them to me, I will have Adrienne post them. It would be a very useful reference for people who are "thinking about" changing carbs. Thanks, Les
Les Bengtson

In the early 80s I bought a triple DCOE setup and head for a 240Z I owned and I had a terrible time trying to setup the carbs for my engine. Although it did run, it didn't run as good as it could. After buying some books and jets and other parts, at not an inconsiderable cost, I finally brought the car to a shop that specializes in Ferraris and other exotic cars that frequently use Webers and let them do the tuning. Although not cheap it was worth the cost as they got the car running 100% better. I suggest you try to find a racing shop or another type of shop that knows and works on Webers. The setups given in books are a good starting point but every engine is different. You could also install a o2 sensor and a air/fuel gauge to see how the engine is running - after you finally do get it running. FWIW, I think it's more than a carb problem although if it backfires through the carb that generally indicates a lean condition or a timing/ignition problem.
Mike MaGee

Usually the toughest part of a weber is getting it sorted for drivability; it's usually not that hard to start the car - as was stated, the weber pump jets will squirt fuel down the throat of the carb which primes it nicely. The idle screws set the idle mixture, the idle jets are for the off idle transition and part throttle driving.

I agree with Daniel, I would suspect the ignition system first, and then fuel delivery.

Mine will start with pretty much any initial timing I've just thrown the distributor in there to get it running and with the intention of setting the timing dynamically after - it started right up. So setting it to the recommended static timing (10d BTDC IIRC) is a good bet.

Next, I would follow some of the advice from the guys here for getting any car running - check you've got spark, at the right time (firing order of 1-3-4-2), check that fuel is getting to the plugs.

Have you seen the car run with the weber on it? Do you know what's been changed or worked on since then? That might give you a clue on what's gone wrong.

Once you've ruled out the ignition, come back to the carb. Most instructions you'll find are talking about older webers, you need a bunch more turns on the idle screws to get rich enough with the newer models (like the 152). 3-4 turns ought to be closer than the 1 1/2 they use on the old ones.

Then, unless the weber is already sorted for the B, or you like to fiddle (and spend money), I agree, find a good tuning shop to get the right jetting for you.

Usually you don't need to touch the float height from the factory, so leave that unless it's been changed - I've never been able to find a good reference for the correct height for 152's anyway. If you post your main venturi size and your emulsion tube type, I'm sure someone here can tell you what jet sizes will get you running reasonably well.

Good luck - stick with it, you should be able to get it running and idling at least.
Mike Polan

Thanks for the all of the help. I will post the jet size (which happens to be the only set of jets I have) when I get home and take them out. How should I check to see if spark is getting to the plugs (do I need a special tool for this? The fuel pump does work it makes noises and fuel come out the line that feeds the carb. The has ran with the weber on it for my father in 94 and start once for me in 00 and ran for 30 seconds till I let off the gas and has not started since. I know the carb was bought in the mid 80's and was not for an MG.
Confused MG Owner

How old is your fuel?

You haven't referred to it and no one else on this thread has either.

If your pertol is 1994 vintage - even if it is 00 vintage, then I would begin by draining the tank and refilling it. The problems you describe are symptomatic off several problems and and stale petrol is included
Marc

Fuel is not from 94 It is from last year.
Confused MG Owner

Confused. It is too old. Run a long line from the pipe going to the carbs and insert it into a large container. Use the electric pump to pump out all of the old fuel and refill with fresh. When you refill the tank, add some fuel stabilizer to the gas. The modern blended fuels will go off in a relatively short period of time. Keeping the gas tank full helps to prevent this, but it can be a problem with cars stored for longer periods of time. Les
Les Bengtson

To check for spark at the plug, remove each plug and re attach wire. Set each plug w/wire on the block so that they are grounded. With the car in neutral, have an assistant turn the key. Look at the plugs as the engine turns. You should see a blue spark from each in rotation. Don't touch wires or plugs while your assistant is on the key or you will get quite a jolt.
Paul Hanley

I too am dealing with a MGB that hasn't wanted to start (just got it running today).

You shouldn't need the carbs to be working much at all to at least get the engine to attempt to fire. So I think it is the ignition (that was the problem with mine, wasn't getting a spark)

This is what I did.
-take out the spark plugs and place them back in the wires. Lay them on the block so that the threads touch the block. As others have said get someone to help crank the car and don't touch anything while cranking. you should see the spark.
-If there is no spark
-disconnect the battery and disconnect the small wire that come out of the wiring harness from the coil (I started with this because I didn't want to touch the distributor and timing). With the ignition on (make sure you reconnect the battery. I fotgot once) check the volts of those wires. It should be near 12 volts. If its very low then the coil isn't getting power. and the cause of no spark.
-check the ohms of the spark plug wires and the one that goes from the coil to the distributor. There should not be a lot of resistance. If there is get new wires.
-On to the distributor. Take the cap off and check inside the cap. It should be clean with no signs of cracks or burns. The contacts of the 4 wires should be nice and clean. The carbon brush in the center should be free moving and not worn out looking (not sure the specs of how long it should be)
-take the rotor off and turn the engine until the plastic part that rides on the shaft is on the top of one of the 4 lobes. Check the gab between the points. For 25D and 45D models it should be 0.014" - 0.016" (mine was 0.050" and was the cause of no spark. what ever caused it to get that far out is beyond me) Changing the gab of the points is very easy and is in ever shop manual (if you don't have one or if those pages are gone let me know and I'll scan then and email them to you) Also make sure the points are clean.
-make sure the cap is put on the correct way.
-check for a spark again. If there is still no spark then all that is left is the coil and I would replace it as I don't know how to test it.
-make sure the wires go to the correct plugs. counter clockwise from the back 1-3-4-2. #1 cylinder is to the rear.
-If you do have a spark and it will not start, spray a little starting fluid in each cylinder (through spark plug holes). Quickly put the plugs back in and try and start it. there should be some sign of life that this point.
-While trying to start try the gas peddle at different places. mine wouldn't start if it was all the way down or up, but wanted to be about 1" depressed.

-Steve
Steven J. Korotky

"check the volts of those wires. It should be near 12 volts"

The coil will only have 12v on both terminals if the points are open. If they are closed the -ve will be at ground potential, a 12v coil car will have the +ve at 12v and a 6v coil car will have the +ve at 6v.

"-check the ohms of the spark plug wires and the one that goes from the coil to the distributor. There should not be a lot of resistance"

Define 'a lot', suppressed leads can easily be 20k.

Flick the points open and closed with the ignition on, you should see a small spark at them and be getting HT from the coil wire.

Burning of the cap contacts and rotor edge is normal and caused by the HT spark jumping the gap. Use an inductive pickup 12v timing light to check the cap and rotor. If you get flashes connected to the coil wire but not the plug wires then either the cap or rotor is breaking down, change both.

You cannot put the cap on the wrong way unless it or the distributor body is damaged.

Number 1 cylinder is at the FRONT of the car.

You should not need starting fluid nor accelerator pedal to start, but you will need an operative choke under most conditions when starting from 'cold'.
Paul Hunt

This thread was discussed between 01/09/2003 and 08/09/2003

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.