With little over 7 to 1 compression, you shouldn't need any additive. If its pinging and or knocking, our timing is set wrong. I would also bet, you are lowering the octane of your fuel quite a bit with the Kerosine additive.
Run the engine at a high idle and slowly dump a cup a straight water down the carb. The steam being made will clean the piston tops of any carbon build up. If it still pings, back the timing down till it quits. Pay no attention to the pointer or timing marks, just get it to quite pinging.
Once you are satisfied its not pinging at anytime, check the timing marks against top dead center of #1 piston.
More octane is wasting money if the engine doesn't need it. Low compression engines do not need much! I would also bet the Marvel oil is gumming up the carb when the fuel evaporates out. Ethanol creates enough problems on its own, don't go adding to it.
