Re: "Why you put an engine on your bicycle?" and best answer goes to...
In the early 60’s a friend had a Sears Moped. I rode his and was sold. Saved up my money from a job picking up golf balls at a driving range (no tractor, picked up by hand) and had enough money to buy a Moped in 1963. Parents said “NO, you’ll kill yourself”.
Graduated from college, got married and had a friend that had a new Honda 750 4 cylinder. Got the urge again. Wife said “NO, you’ll kill yourself”. That was an interesting statement since at the time I was an Air Force pilot flying jets over Vietnam. She was OK with that, no danger there. Found a Harley Davidson 90cc street/trail bike used and convinced her that a 90cc wouldn’t kill me. Bought it and later quietly upgraded to a Honda CB360T. Early 80’s came and kids, work, etc and I got out of the motorcycle business. I gave up my motorcycle endorsement on my driver’s license.
Now in my “Old Age” I got the urge for bugs in my teeth again, but I didn’t want to go through the hassle of a new license, insurance and expense that goes with owning a motor cycle. I saw an ad on the internet for a bicycle motor and started doing some research. I ended up buying a Schwinn Landmark from Wal-Mart and a friction drive kit from Stanton. I now have “low speed” bugs in my teeth but it is the same fun that I used to have on my Honda at 70 mph. Best money I ever spent.