I just bought an 05 yamaha yfz450 this is the first yamaha i've owned but i have a problem i hope you yami guys can help with
my yfz pops when you open up the throttle about 5 or 6 times before it goes but at low speeds or idle it is fine if anyone has an idea or have had this problem before
thanks for your help in advance

 

Any mods? Aftermarket exhaust? lid off? filter?

Any of those will change air flow. Try screwing you fuel screw out a turn on the carb.

 

The only aftermarket parts on it is a gyt-r slip on exhaust
i will try messing with the air fuel screw and let you know if that works

Thanks

 

sounds like maybe somebody didnt rejet it for the pipe, you might be able to make it go away by adjusting the fuel screw though.

 

Definitely. If you didn't rejet you probably should, especially if you hear backfiring. Popping on decel will be in the fuel screw.

 

well i tried adjusting the fuel screw and that didn't help
so my next thing is to take the carb off and see what is in there for a main jet and a pilot jet does anyone have an idea what should be in there with that slip on pipe i live in wisconsin if that helps
thanks again for your help would like to get it figured out before we leave on our trip next weekend

 

i just got done pulling the carb and what is in there for jets are
42 for the pilot and 165 for the main any suggetions on it

 

Wouldn't hurt to step up to 45 on pilot. should be able to get by with what you have, I did. I'd def go up on that main. 170 maybe 172. Better rich than lean. 2 or 2.5 turns out on idle.

 

Airbox lid on maybe 170? Here is a thread strictly yfz jetting.
ATV Riders Forum - YFZ450 Jetting .

 

Thanks i will give that a try tomorrow and let you know what happens
Thanks Again