what brand of fuel are you using for starters? using a low quality fuel with a high oil content can make the exhaust smoke very thick and also make it look like alot of fuel coming out of the exhaust, where in reality it is just unburnt oil. if your fuel is a good brand or mixed by a reputable seller then it sounds like your engine is too rich. the JP engines are very sensitive to any changes to the needle valves as the are modified internally. start by getting the engine upto heat. run the engine up and down a straight area then bring the car to you and pinch the fuel line about 2cm from the carb. the engine should for about 2 seconds then rev up a little bit then stall. if it does this your low speed needle is set correctly.if the engine revs up as soon as youpinch the fuel line this meas that the low speed needle is set too lean. start by turning the low speed needle out 1/12th of a turn at a time. if the engine idles any longer then 5 seconds when you pinch the fuel line then your low speed needle is set too rich. turn the low speed needle in about 1/12th of a turn at a time until you get the described effect above.once this is set you can start to tune the high speed needle. give the car onther run on a straight surface for about 30 seconds. if the car feels sluggish and still blowing excess exhaust smoke turn the high speed needle in about 1/12th of a turn. give the car another run, and if the car feels like it has a bit more power repeat this process till there is a slight amount of smoke coming out of the engine or until the engine sounds like it is revving well all the way through the rev range. once you have reached the optimum setting back the high speed needle off 1/16th of a turn. i hope this helps.