I have a kings motors bushing engine this is not a powerking engine .
It is on its second steel frame bike.
In the summer temps are around 54 C or 120 F .
I use a Castor synthetic air cooled oil at no less than 20 to 1 .
Do not lose the throttle going down hill.
Do not stop at lights for long you need the air flow.
Warm it up slowly.
A bushed engine may be he better engine compared to the funky roller bearings in a Chinese motor.

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Motorized bicyclist