Mine starts to hesitates at 1,500 miles occasionally and get worse over time, roughly and backfiring when apply a small amount of twist at handle, near idle and hesitates roughly. Idle at cold start was not in same RPM like before, slighty low, causing some stalling. I go for two options, valve adjustment or dirty throttle body. I remove all the hardware to gain acces to the valves at 6,000 miles and found that i don't have the tool to adjust the valves, so I go for plan 2. With the throttle body cleaned all roughtness and backfiring DISSAPEARS. I think that, because this kind of bike has no oxigen sensor, with a small twist of handle, the TPS send the signal to computer to increase inyector pulsation, but there's no enought air to burn this aditional fuel 'cause dirty throttle body, causing hesitation and unburned gases to explode on the muffler, causing this backfire effect. Also, my idle RPM raise again to 1,400 RPM.miket said:I love my 400, but it backfires. All services are up to date; I clean my own air filter every 1000 miles; I use the best quality fuel I can get. Any suggestions?
First, mine is a AN400 with 7,859 miles.easylistener said:Put standard 87 octane gas and this will help. The problem with high octane fuel is it won't burn all the way in these scooters. Thus leaving raw fuel enter into the exhuast and puddle. When the exhuast gets hot it will cause the fuel to cumbust. This will help.
Other possibilites the compression release is sticking or the valves are to tight.