when i start my 1977 mgb it ticks over ok then the revs start to climb the pistons in the carbs lift themselves they have the right amount of oil and grade


Asked by Jun 17, 2013 at 01:58 PM about the 1977 MG MGB Roadster

Question type: Maintenance & Repair

when i start my mgb it ticks over ok but after a min the revs start to climb if i unscrew the carb dip stick  and lift it and replace it the revs die back down again for a few mins then climb again the pistons are lifting by themselves

5 Answers

"carb dip stick"...kinda lost me on that one, I know these have special vacuum controls goosing the the throttle open smoothly, are these the things that you are changing? do not understand~


the dip stick in the top of the carb with black top well kind of dipstick, i just bought the car it was running rough i got it to run smooth but now the revs climb by themselves the pistons in the carbs are lifting and bringing the revs up,

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its called the dampening valve it has a black plastic opr brass top if i unscrew this and lift it slowly then push it back in the revs drop for a few mins then pick up again

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want to help, but this is uncharted territory for the judge~


What sort of carbs are on your car? SU's or Zenith Stromberg? A bit more info would go a long way. Also these constant vacuum carburettors are quite sensitive to other faults, things like poor compression or offset timing can have a huge effect on idle speed, so I normally start with checking those before even looking at the carbs. From there on I check oil level in the dashpot (where you took out the little dip stick, it should be filled pretty much to the brim with SAE 20 oil). Then a quick look at the throttle spindles to make sure there's no free play or vacuum leaks and from there on I normally go for a carb tune (get out the synchroniser and tachometer and get it set up right).

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