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MG MGB Technical - Wont rev & backfires

MGB GT 1978, was running fine until today: now it backfires and will not tick over. I have checked the following: all pipes are correct, Points, plugs, cap, leads (all new), I changed the coil,I checked the valves, the carbs appear to be fine... HELP (Bad earth?)
P Hobson

Check for vacuum leak or bad condenser. Good luck - Dave
David DuBois

The only other thing I can think off is that the battery box was welded recently and if i am not mistaken the earth (ground) is through the battery box
P Hobson


Check you point dwell and ignition timing.
Backfiring is usaully a sign of timing that is off.also make sure the firing order on the cap is correct.


Jim
ja adams

Had this symptom once with a falty vac unit on the distributer.

Ralph
Ralph

tried swoping the dizzy & it makes no dofference. It will run (not very well) on full choke - Carbs?

Or perhaps a head gasket ( compression fine when I tested)
P Hobson

Maybe the welding affected the operation of the fuel pump? It sounds like you're starving for fuel.
Jeff Schlemmer

Back to square one with this b*****D car. I have replaced the points plugs, cap, rotor and condenser and can can get it to idle , but when I go to rev it it just dies unless i give it full choke. Have also checked the carbs and fuel pump and the inlet manifold for leaks. Is the new condenser dead as well and is there anyway of checking them, or does anyboby have any bright ideas.
P Hobson

Check the ground wire (inside the dist) for the breaker plate.
Hook up a timing light and watch as you accelerate the engine to see if the spark is going away. If it is then it is an ignition problem. If the spark does not break up then it may be fuel or the timing chain may have jumped a tooth.
If compression checks good then it is not the timing chain.
It sounds like fuel or gas to me.
Good luck.
Steve
Steve

You checked the fuel pump for leaks, but did you check it for proper fuel delivery? I forget what the time is, but you can test it by the length of time it takes to fill a quart jar.
The other problem could be with the needle/float assemblies. It sounds like you are getting no fuel.
Jeff Schlemmer

Should deliver *at least* 1 Imp pt per minute with negligible bubbles. Faulty needle or float not letting sufficient fuel through would normally let the engine run at higher revs for a while as the chamber emptied, then start to stumble.

Have a timing light on the coil lead and plug leads when you rev it and it dies. If the light continues to flash on all leads it is almost certainly fuel. If it stops flashing on the plug leads but not the coil lead then the cap and/or rotor are breaking down (replacements noted). If it stops flashing on the coil lead as well then you need to go back to the primary circuit with a voltmeter.

With things like this always go back to first principles. Telling yourself certain parts are new so it can't be them is an exercise in frustration, new parts can be faulty as well as old.
Paul Hunt 2

Your inquiry regarding the condensor is a valid one. I had new condensors "right out of the box" fail and used the old unit. The old unit worked just fine.

Good luck and let us know how this turns out.

cheers

Gary :>{D
79 mgb
gnhansen

This thread was discussed between 19/08/2006 and 25/08/2006

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