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 - Lumpy running at low revs

My B has come back from its annual service running very lumpy below 1200rpm. By lumpy I mean almost misfiring. It was fine when it went in.... All previous services by this mechanic have been perfect - he was an apprentice on B's in the 70s. He has had it back and agrees its running badly and will look at it next week. Timing, valve clearances all check out OK.
I am sure that this is simple..... Any thoughts would be welcomed.

Thanks

Dave
David Tolcher

Offhand... if the carbs are synched OK and the valves and timing checks good, then it sounds like
the mixture may be weak. Before fiddling with the carbs, however, check for a loose vacuum hose.
Daniel Wong

have you tried

making sure vacuum advance pipe reconnected

if its on hs4 su, that one jet is not stuck in the choke, i.e. lowered ,position

both carburetter pistons free

carb dampers filled with oil

air filter to carb gaskets properly secured, if one end does not have the bolt through it can slip and obstruct the airflow

contact breaker gap correct , if too narrow this is often a source of low speed miss

good luck, I'd be interested to know the solution


christopher storey
christopher storey

Also check that the float valves are set correctly and both are properly seated in the bowl covers. Sometimes they don't get snugged up when replaced, vibrate loose and either change adjustment or fall out.

As per Christopher's comment on the jet linkage - also check that the plastic base of the jet has not crumbled away from the screw to the connecting linkage. This happened to me once and the car definitely ran lumpy! Good luck!
Bob Muenchausen

This thread was discussed between 06/04/2002 and 08/04/2002

MG MGB Technical index

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