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MG Car Repair/runaway acceleration on startup


The new SU installed on my 1980 MGB, made for the US is an HIF-6 carb. I believe it to have a 1-3/4 throat opening. One note, the new throttle cable I installed gave me a little trouble installing at the carb end. The cable end,  which has a solid cylindrical shape to it didn't fit without my using a little force to get it to insert into the mating part on the carb. I didn't like that but it did seem to operate properly...perhaps not. The throttle butterly lists quickly and almost fully upon starting and staying way up. That's way the rapid, runaway acceleration. I even tried to lower it with my finger and it wouldn't go down. Thanks in advance for staying with me here.

Hi Bill.  You are correct.  A HIF6 carb has a 1 3/4 inch diameter butterfly.  Like I said before, with the choke pushed home and your foot off the throttle the butterfly should be almost shut.  If you cannot shut it completely by using the throttle adjusting screw then the throttle cable is wrongly set up.  My setup has a cable adjuster so I can alter the length of the outer cable.  Do you have an adjuster anywhere?  Possibly there is a clamp at the pedal end that can be moved up and down the cable.

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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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