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I would suggest getting the .18 piston, sleeve, connecting rod, piston pin and turn it into an .18. I did this and it worked great and got several gallons out of it. Even if you just repalce the stock piston/sleeve you should also replace the connecting rod it is cheap 5$ insurance.

When you do put in a new piston and sleeve remember to set the carb back to factory settings and re break in the motor.

rolland