QuestionQUESTION: i own a 1971 USA model MGB, fitted with a 123 electronic ignition system and a peter burgess fast road head,the car runs really well except when running at a continuous speed where very little pressure is necessary on the gas pedal,the engine then becomes very erratic,making it a most uncomfortable ride,accelerating cures the problem.
ANSWER: Hi James. This is an interesting problem. My immediate reaction is that the carburetter dashpots are empty and you need to top them up with engine oil.
My second thought is - do your carbs have a small circular valve fitted to each butterfly? If so, solder them closed.
I had a similar problem on a 1955 MG TF fitted with a half-race camshaft, and I believe that some MGA twin-cams also had it. I cannot guarantee a cure, but if all else fails you could give this a try: The HS4 carbs on your MGB each have a fork on the throttle spindle, and usually these are adjusted so that both carbs open simultaneously. Try staggering them, so that one carb opens slightly earlier than the other. Just unclamp one fork and re-position it.
Please let me know how you get on.
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QUESTION: thanks for your quick reply, but the dashpot oil is at the right level and the circular valves in the butterfly have been closed, which is why i'm a bit stuck as where to look now, also the problem is not consistent some times seem to be worse than others, but i,m certainly convinced it,s fuel related. thanks again
AnswerHi James. It could be that one of the carbs has a worn float chamber needle valve. At slow speeds, it could flood the carb. Remove the valves and check for a wear ridge.
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Have you still got the original FX carburetter needles? They are a bit weak for a Peter Burgess cylinder head, especially if it has raised compression. Try needle number 5 instead.
