Greetings, My name isXXXXX and I am here to help the best I can. My goal is 100% satisfaction. Let's get started.
OK, here is the weird answer first
It sounds to me like a twin cylinder engine that is only running on one cylinder.
Start the engine and then, with a good set of insulated piers, pull one of the spark plug wires off and note how the engine runs.
If the engine dies, then you know that the other cylinder is not working.
If the engine runs the same, then the cylinder that you removed the plug wire from is not working.
If the engine stays running, but runs much worse than it did, then both cylinders are working.
What could cause one cylinder not to work?
1. Bad ignition coil
2. Valve rocker arm came loose. or bad valve.
3. Broken connecting rod on that side,.
4. BAd spark plug on that side.
5 Blown head gasket on that side.
If this is not the problem, contact me and we will look at this again.
Or, the problem coul dbe so simple that you have a problem in the carburetor
where the needle and seat are not mating correclty and the gas is not being shut off all the way when the bowl is full
ALSO, SMELL the oil
see if the Oil has a gas smell to it
Let me know what you learn