I have a 2005 Yamaha yfz450se that has recently started back firing. What is causing this? The bike has been jetted, k&n air filter, and a pro-circuit Ti-4 pipe. Any help is appreciated.

 

what rpm does it do it at?

 

Mostly occurs when coming down from a high rpm. Example would be when the bike is in neutral I'll give it a shot of throttle about mid to high rpm and when the engine is coming down from the rpm the pipe will back fire or pop.

 

does it do it once or all the way down through it?

 

i have a similar problem with my '07 YFZ450se, its piped, jetted, air filter and air box lid removed and when i let off the gas from high rpms it backfires multiple times while dropping to an idle, the only way to avoid it is if i let off the gas slowly, it happens more high end on my quad though.

 

check your jetting.. it may be lean or really rich.

 

Mine does it just once but sometimes twice, how do I tell if I'm running to lean?

 

in response to breck, i know for a fact that your pipe will start to go red hot if it is running lean. try runnin it at nite and look to see for any signs that the pipe is running hot. you could try pulling ur airbox lid if it is running rich?

 

i would like to kno if there is a better way for checking jetting tho. i was told you could tell by the spark plug, except from what i have been told u gotta pull the spark plug rite after u run it and i don't get how you can do that because you have to pull off plastics and the gas tank to even get to the spark plug...

 

ya plug chops.. run it at 1/8 throttle.. pull the plug check the color... run it 1/4 throttle pull it.. check color.. 1/2 throttle... then 3/4... then WOT..
you're going for a toast color

http://www.dansmc.com/Spark_Plugs/14.jpg soemthing along those lines.