you could have a air leak like at the exhaust gasket abd base gasket or the crank seals you can take a propane or starting fluid and spray around thess areas after it warms up and if the idle goes up you have a air leak. A air leak is when air is getting inside the motor from some where besides where it supposed to (the carb) and can cause your motor to run lean and get hot and soft seize, if your mix the oil yourself you need to increase jet size by 3 % try the next size up just to see what happens
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