Just bought an 05 yz250f that had just had the engine rebuilt with new alloy piston, new valves, new timing chain ect. Bike rides fine and goes hard but back fires when backing off the accelerator and there is a noise that sounds like a chain saw when it is revved. Anyone have any ideas?
Yz250f noise and backfiring
- Thread starter Herm2222
- Start date
- Nov 25, 1999
- 7,926
- 43
The backfire can be several different issues but if it has been recently rebuilt here is one direction to go. The accelerator pump duration is likely fairly long maybe 1.5 seconds or so. Adjusting the duration to around .5 to .75 seconds will help the acceleration and reduce the backfiring. Proper tuning will help reduce the backfiring more but most likely you will always have some.
The accelerator pump adjustment takes a small bit of modifications and will require a bit of research. Well worth doing and will help you really get to understand the bike.
The accelerator pump adjustment takes a small bit of modifications and will require a bit of research. Well worth doing and will help you really get to understand the bike.
