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MG MGB Technical - Help, Please!! My B is running like a farm tractor

Hello,
I drove my car Saturday afternoon, it was running great. Parked it in the drive. Later went to move it into the garage, and "all of a sudden" it's running horribly!
Here's the symptoms:
Almost will not start
Sounds like it's running on 2 or 3 cylinders
Idles only with choke out
Rpms drop way down when you try to give it gas
Vacuum gauge reads low with needle bouncing rapidly
(Haven't been able to run compression test yet.)


I completely rebuilt the engine about 4 months ago. No (real) problems until now. Wiring all new. I just installed a new distributor from Brittek, no difference. What gets me is the "all of a sudden business"??!!

What might I look at?
Does this sound like fuel or ignition?

Many thanks for any advice, Dave
David Steverson

Hi Dave.

I suggest you look for air leaks around the inlet manifold.

Don
Don

Dave,

Check that one of the SU pistons is not stuck in the up position.
Just remove the damper caps and check for free movement using the piston lifting pin.

Mick
M F Anderson

David,

You may want to check the fuel filter/pump. The fact that choking it allows it to at least idle could indicate lack of fuel.

Cheers, Doug
Doug Keene

Jsut a quick list of things to do, I've found it best to start from scratch and narrow it down.
If you take the air filters off you can check the pistons are not stuck. Also check the throttle and choke cables to make sure they are not binding. Next, I'd pull the dist. cap and make sure it's dry and nothing inside has come loose. Check the gap too. Also, check you have the wires in the correct order. You may want to do a compression test too.
If all of that is good, try running it and removing the plug wires one at a time. If it's fuel and you have dual carbs, you'll find that either 1,2 or 3,4 make no difference if connected or removed. If so, then the carb connected to that side of the engine is probibally not getting fuel. If they all cause the engine to drop in RPM's when removed, pull a plug and ground it to the block and turn the engine over. See what the spark looks like. It should be visable. If the they all have a strong spark, it is probibally fuel pressure related, either filter or pump.
I'm sure I rambled a little, but I have found if you do everything in a logical order you'll eventually narrow it down. Also, if you have never messed with the plugs while the car is running before, you should know you'll get a fair shock as you pull 'em. You'll probibally want to use an insulated tool to do it. Hope this helps.
J Arthurs

Check your spark plugs.
Dauntless

Does the new distributor have an electronic ignition? If the trigger
(optical or magnetic) comes loose, the timing will be
way out causing your symptoms.

Ronald

David-
Your "Vacuum gauge reads low with needle bouncing rapidly" and "Sounds like it's running on 2 or 3 cylinders"? Check the oil in the damper tubes of the carburetor pistons. Check the damper rod, too. Sometimes it's the little things........
Steve S.

What year is it? Could be that the anti run on valve found on later cars is stuck open.
R. L Carleen

I had an "all of a sudden" problem once - the distributor collar had loosened. It was a simple matter of getting it started (roughly), twisting the distributor until it sounded good and cinching it down.

When I scooped it following, the timing was spot on, too.

Good luck!
John Z

Plugs, wires, dizzy, gaskets and all hoses, etc., all check OK?

A low and bouncing vacuum needle would lead me to look for a compression problem.
A compression test is in order here and will help prove or discount this.

Fouled valve(s)?

Since your car was running just fine a moment before, the sudden onset of your car's ills has
me thinking that it could be as simple as an errant bit of carbon getting caught on one of the
valve faces or seat. Hey, carbon deposits as it can sometimes become as hard as glass
and become very stubborn to clear.

When this happens, the valve(s) are prevented from closing fully, compression bleeds out on
every stroke, and the gases whoosh in & out of the partially closed valve(s) causing your engine
to shake about (from uneven firing) and the vacuum meter to have palpitations (from the
whooshing gases).

Try letting your engine gargle on a healthy dose of upper cylinder head cleaner or give it
a few good shots of Gumout into each carb throat (while you rev the engine up and down).

Also try shutting off the engine during mid-application, and let the stuff soak in for 15-30 minutes
or so to give it a better chance to soften any especially hardened carbon deposits.
Daniel Wong

Maybe you should look closer at your problem. Everything may be okay, you may just be driving a Triumph.
Larry Wiseacre

Many Thanks to everyone for your help and advice.

Turns out the problem is where the fuel line enters the float chamber from the jet. The rubber seal had gotten twisted round a bit and eventually blocked the fuel supply to the rear carb. I guess it just chose that moment to make it's attack!!

The jets came in a kit from Vicky Brit and did not seem to fit just right going into the float chamber.
My new (and hopefully better) jets are due in from Brittek soon.

This website is truly worth it's weight in gold (not sure how much a website weighs??) !!
Thanks again, Dave
David Steverson

This thread was discussed between 13/02/2003 and 16/02/2003

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