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MG Car Repair/HIF carbs


Hello Barrie, I have a hard time starting my 73 B after it has run for a while, I need to hold the gas pedal to the floor while turning the engine. It always starts but takes a while, runs rough and then it is good to go. Timing is set to 11 degrees @1500rpm and it has Pertronix electronic ignition. I have a new heat shield in place as well. I suspect carb setting possibly to rich? Any feedback is appreciated. Thank you.

HIF Carb
HIF Carb  
Hi Andre

I agree that it sounds like the carbs are set too rich.  This could be due to several problems.

I would start by checking the mixture setting.  With a warm but not hot engine, check that the choke is fully home and then test each carb in turn by lifting the PISTON LIFTING PIN (item marked 4-10 in the attached diagram).

The engine speed should rise and then drop.  If it rises and stays up, then it is too rich.  If it drops without first rising, then it is too weak.  Both carbs should have the same effect.  If one rises more than the other, then the carbs are not correctly balanced.  

To weaken the mixture, turn the adjusting screw anti-clockwise, but do it in VERY small increments, like 1/4 of a turn or less.  (Adjuster is item marked 6-8).

Try this out and let me know what you find.

(Diagram reproduced courtesy of Burlen Fuel Systems, Salisbury, UK)

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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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