MG Car Repair/Mgb 74


What is the proper float level for my 74 mgb su hif carbs.? Have read that float levels should be set one mm. Below carb body at low point on float. Does not seem to be correct, please help
Also when car is hot, it will not start? Any ideas? coil?

Hi Robin

You are correct that the float must be set with a 1mm clearance between a straight edge and the dip in the middle of the float.  However, you must set this clearance with the carburettor turned upside down.  The float will therefore sit 1mm ABOVE the carb body when fitted to the engine.

Most hot restart problems on the MGB are caused by excess heat in the engine compartment:

1) Check that the heat shield between engine and carburettors is complete and undamaged.

2) The fuel line runs underneath the heater.  There should be a small metal shield to protect it from the heat of the engine.

3) Check your engine timing.  If the ignition timing is retarded this will cause overheating.

4) If you still have a long rubber seal fitted to the rear edge of the engine compartment, remove it, cut it into 3 pieces and re-fit parts 1 and 3.  Throw the middle section away.  This will allow more hot air to exit the engine bay.

Please let me know how you get on.  

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Barrie Jones


MG Sports Cars from 1949 to 1980 - Including MGB, MGBGT V8, TF1500, TF, TD and modern Midgets. I also specialise in SU carburettors, Lucas wiring, suspension, steering & brakes.


I have owned my 1955 TF1500 since 1966. Technical specialist for the TD and TF with the MG Car Club T Register. Also owned 20 MGBs and currently own an MGBGT V8. Written 3 books on MGs and produced a DVD on how to strip and rebuild the TD/TF gearbox.

MG Car Club.

Barrie's Notes on the 1953-55 MG TF (author). /=====/ Barrie's Notes on the MGB (author). /=====/ Barrie's Notes on the MGB GT V8 (author). /=====/ The Essential Buyer's Guide to the MG TD, TF and TF1500. (author)

M Phil, C Eng, BSc (Eng).

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