Re: fuel line up against spark plug
dag has a good idea; try a shorter plug. I've had good luck with the Autolite 2976. I built a 24" bike for my nephew and the plug clearance to the top tube was like yours. If not for the short plug he would have to pull the engine off to get it out but the short plug worked great. The Autolite should be available at most auto parts stores.
Age and Treachery Will Always Triumph
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