When you put the bike up for the night, how hot is it when you shut it down? One possibility is that the fuel is boiling off in one of the carbs, is traveling through the open valves, and building up and condensing in the exhaust pipe/muffler.
When you first fire it up, as soon as the hot new exhaust hits the gas vapour or gas condensation, it fires that up, and you have the backfire boom.
Might also be caused by a float that is a little too high, and gas is getting into the exhaust sytem that way when you shut down.
Try giving the bike a 1 or 2 minute cool down period after a hard ride.
I think it may be a reason. Actually most of the time the cooling fen is working by the time I shut the bike down. If I ride for some time in the first gear down the block and by the time I entering the garage, it gets hotter. The fen may even work after I’m shutting it down.
A forum community dedicated to all Kawasaki motorcycles including the ZX-6R, KLR 650, Ninja 250, Ninja 250R, and Vulcan. Come join the discussion about performance, modifications, troubleshooting, maintenance, and more!