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MG MGB Technical - Weber Problems...

Hello All,

I've recently replaced the Zenith/Stromberg carb on my '78 MGB with a Weber DGAV. Now I am having an issue...

1) The car starts perfectly (first crank every time).
2) When first starting the car the idle is fine.
3) When I juice the gas, it gives a bit of hesitation and occasionally backfires through the carb (not always just sometimes).
4) If I take it for a drive it runs fine for about 30 to 45 seconds and then I start getting really bad hesitation. The longer I drive the worst it seems to get. When getting back from the drive the idle drops real low until the car sits for a bit...then idles normally.

I have a friend who is a mechanic that came over this evening to take a look...after a couple of hours of fine tuning he is convinced that it is simply not getting enough fuel. So my questions are...

1) Is the stock fuel pump strong enough to feed this carb?
2) If not what is recommended?
3) My friend also took a look at the distributor and it seems to have a little play in it (and the car never really idles smoothly). He said this could be caused by the play, as the points will widen and tighten as the car runs. Would this mean it is time for a new distributor? Can anyone recommend an affordable solution?
4) Is there anything else that I should be looking at for the issues that I am having?

Thank you all in advance,
B Howard

B,

The standard fuel pump should be more than able to supply your engine with the necessary fuel, if it is working ok.
There must be something else wrong, there are some people on this board who might be able to help with it...

Alex
Alexander M

if your carb is hesitating and spitting when you apply the gas, you need to turn the mixture screw in, (clockwise), just a little more. Also, you need to make sure you have the heater hoses attached to the bottom of the intake, if your manifold has it.

I have used several of the Webers over the years and the fule pump has always been plenty.

If your car didn't have the hessitation or back fire with the old Zenith, then it will not be the distributor, as it is the same set up as previously.

I have had the same back fire / spitting from the carb, and turning the crew in a little more has always cured it.

Good luck,
DT
Danny T.

The stock fuel pump should be adequate, but it sounds to me like something is preventing sufficient fuel supply to the carb. If you are certain that the fuel filter is clean and the fuel pump can deliver it's requisite volume and pressure (1.5 - 2 pints per minute at 1.5 - 3 psi), then you will need to take the top of the carb off and make sure that the needle and float are not binding and are allowed to move freely. Then check the float level setting to insure adequate fuel level in the carb - I can't remember what the setting should be at the moment.

What I have found is that my two Webers like a lot of initial spark advance, at least 15 or more degrees BTDC; but you have to make sure that the total advance while running (without vacuum advance) stays below 38 degrees or less - depends on fuel quality. Also I set the idle on my cars at 8-900 rpms. You may have to adjust the accelerator pump linkage so that you get full pump travel from idle on. With the engine not running, look down the carb to see if the accelerator pump squirts fuel into the engine - if not, there's another good source of hesitation and backfiring off idle.

Wayne
Wayne Pearson

www.webercarbs.com. These folks will give you info on basic weber set-up. I'm running a 45 DCOE & had to sort out several issues before the car ran like I wanted. They also have a Tech Line & FREE SHIPPING.
Good Luck.

Dauntless
Dauntless

Excellent...My friend is coming over tonight with a timing light and Fuel pressure gauge...so hopefully we can get this thing running properly with all of your suggestions. Thanks to all. On a brighter note...at least it looks better than the old Zenith did ;-)
B Howard

I was just looking around at some other posts and now have another question...someone had told me to block off the canister hose that went from the canister to the old carb (as it wasn't needed anymore). Is it possible that this could be causing an improper vent for the fuel and starving the carb?
B Howard

How do you have the float bowl vented? .
Dauntless

Ummm...I'm not sure to be honest...what should I look for?
B Howard

I'm sorry :-( I was having SU HIF brain fart. Your new carb is vented at the top of the carb under the air filter(stupid me). I kinda misread your question. You could try running the car with the gas cap off & see if it runs any better if you feel there is a fuel tank vent problem causing fuel starvation but it dosen't sound like that's your problem to me.
Dauntless

O.K. so capping the canister isn't a problem then?
B Howard

Nah.
Dauntless

I would doubt that capping the previous vent line from the ZS carb would be affecting fuel feed -- especially since you describe that running conditions change as the car warms up -- but easy enough to pull the cap.
When I purchased my 76 earlier this year, it was not running but I was told it had carb problems. Until this week I have not done anything to the carb except clean the outside. I found similar problems, missing, backfiring, etc, all related to the ignition/timing
Suggest you
-check your installation to see if any possible vacuum leaks
-set the timing at 15 degrees advanced, confirm that the mechanical advance is working and also the vacuum advance. If no vacuum advance, is the carb port capped?
If you have been adjusting the carb idle mixture screw, you might want to set it at 1 1/2 turns out as an initial setting.
Let us know how you progress --
Regards,
Dennis
D F Sexton

Was the car running ok before the carb was swapped? If so it's likely the carb settings. I've read on a lot of threads that the needles and jets need changing in the webbers to get them working correctly with the B engine.

Also if the car did have similar symptons before the swap, then the distributor is well worth swapping if its original to the car. I have just this week changed mine. I was getting very similar symptons with my old distributor on HS6 carbs.

This one has given the engine more punch, it idles smoothly and the spitting back through the carbs has gone. Basically it had a lot of play in it and Vac advance was working over time. I think due to week springs. The recon unit cost me £57.00 although I don't know if the supplier ships to Canada as the local motor factors sourced it for me.

Hope this helps,

Brynmor
Brynmor LLoyd-Griffiths

This thread was discussed between 02/11/2004 and 03/11/2004

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