Pull the plug again, connect plug wire to it, ground threaded part of plug to valve cover and turn engine over to see what color the spark is. If it is blue, spark is good. As far as the choke goes, here is a breif explaination of how it works. When the engine is cold the enrichment needle is retracted allowing fuel thru the enrichment jet. As the engine runs and 12 volts is supplied to the enrichment valve this heats the valve causing the needle to extend blocking off the enrichment jet. If when you start the engine it runs fine than progressively gets worse as engine heats up I would than suspect the choke to be bad. To check you would pull the enrichment valve and connect to 12 volts and watch that the needle extends the entire travel. If your spark is good make sure you have no vacume leak at the intake. This will cause a no change when adjusting the air fuel screw. The intake could have developed a crack when you removed the carb, or the sealing o-ring could be broken, and or cracked insulater. Once you have determined a no leak vacume than I would check the needle /seat for leakage and the float level. When the kart is first started and the choke is enriching you will have a rich plug reading. Try taking it on a run at full throttle popping spitting and all for about 1/4 mile at full throttle than without letting off throttle shut down engine never letting foot off throttle until engine stops, than pull the plug to read it. If it is white/ lean than chances are very good you have a vacume leak. You will also want to check the valve adjustment setting both intake and exhaust to .003-.005. Give me a call if problem still exists. TOM
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