I have probably made a 750 backfire a few Hundred times..
Then one day while riding home at night it blew out about a 3/4 inch chunk of headgasket..
.. if I got on the throttle flame would come out of the gasket surface... After pulling the motor to fix the gasket, I hardly ever did that anymore..
Best way to scare the shiite out of yourself..,
Working on my bike in the carport, had ignition on, and points cover off. Opened the points with a screwdriver, and it backfired, probably louder than it ever did..
.. & I was not expecting it.. Geez that was loud..