The obvious answer is to junk the carb and fit a Weber,
But there is a possibility that it is just the waxstat that is stuck on your pooberg carb, this can sometimes be fixed by removing it and placing it in a pan of boiling water, but by the time you have messed about doing that (and it may not work) you could have fitted a Weber and be off round the block and back home with a bigger smile than usual on your face, as the Weber gives about another 5 bhp and better fuel economy. [
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