Do all the basics first... Start with your air filter, make sure it's clean and properly (not excessively) oiled, re-pack your silencer - this is much more important than most people realize - Make sure the float height is correct, if it's not right, you will never get the jetting right. Check the operation of your power valve, there are several posts on how to do that here... check the timing. you can either use a degree wheel or BTDC measurement. OOps! I forgot to mention the reeds, If they're warped or chipped it can make jetting seem bad... I would also suggest that you might have a bad or worn right -side crank shaft seal. This would most certainly foul a plug and make the bike run rich and oily. They're hard to check unless you have a way to pressurize the crankcase - you might be better off taking it to a shop for that, (or maybe not...) Lastly, you might just need a new piston and rings, do a compression check and compare with some others around here. But most importantly, Don't try to change everything all at once, this usually leads to confusion. Try cleaning and re-packing first so you have a good starting point, then make one change at a time until you get it right. It won't take long (it's a 2 stroke! there ain't many moving parts
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Be patient, and good luck.
'TOOL