"The only 4 stroke moped I know of is an AMI Indian. I happen to own one and there are valves and lifters on the top o the cylinder head. Normally I would say you have a 2-stroke but typically the oil viscosity is not an issue because it is mixed w/gas. Check to see if the oil is for the crankcase (Usually for 4 Stroke)or simply for the gear lubricant. Usually this is ATF trans fluid. Best way to check is to remove the spark plug and turn over the motor. If the plug fires every time the piston comes to the top of the head its a 2 stroke. If it fires EVERY OTHER TIME, its probably a four stroke. Be careful, and make sure, you never want to run a 2 stoke w/o oil in the gas. If you run oil in the fuel of a 4-stroke you will loose some minor performance and probably foul the spark plug. My recomendation until your positive treat it like a 2-stroke and mix the oil. Good luck. "