Re: "Why you put an engine on your bicycle?" and best answer goes to...
Someone stole my weedeater and left the engine!
I didn't put the engine on there. I had the bike parked in the shed for a few days beside the engine. When I went to take a ride, I found them both like this!
This is a classic 1908 motorcycle, not a bicycle. It has just been well taken care of. I bought it new!