I have a 04 660 it is jetted and aftermarket pipe (curtis sparks) and air filter. Last month I cleaned my carbs good, drained and flushed the gas tank, and cleaned the air filter. Rode it and it ran perfect all weekend. Yesterday, a month later, I started it up and it back fires into the left carb and you can see the flame. The boot is connected to the carb but stretches it on back fire. Never did this before and had it for 8 years and I took apart carb many times and this is the first time. Thinking it could be mixture or valves. I read backfire like this can be result of low mixture? Or could it be float valve sticking, spark plug. I did not get jets mixed up cause I only take one out at a time, clean and put back in. any ideas?
thanks everyone!