fmf jetting for 426

[danomx69]

i just put on a fmf powercore silencer and a power bomb header....it ran fine untill i opened it up on the dirt...it was backfiring like crazy.....do i need to rejet it?..ive never jetted it b4 so i would not kow how to do it...is it dificult?...what would i need?..any help is appreciated..

[Doug.]

i just put on a fmf powercore silencer and a power bomb header....it ran fine untill i opened it up on the dirt...it was backfiring like crazy.....do i need to rejet it?..ive never jetted it b4 so i would not kow how to do it...is it dificult?...what would i need?..any help is appreciated..

How bad was it backfiring? On decel or acceleration? Did you use hi-temp silicone to seal it? Might be an exhaust leak.

[642MX]

Sounds like an exhaust leak to me. My bike didn't require any jetting changes when I got my FMF system (powerbomb header & Titanium 4 muffler), I do recall having to adjust my fuel screw a little bit though.

[danomx69]

it was backfiring on decel...its not leaking at all...its all sealed up

[642MX]

it was backfiring on decel...its not leaking at all...its all sealed up

Okay, so your lean. Back the fuel screw out 1/4 turn and try that.

[barch88]

What size pilot jet are you running?

[gbalias]

does the powerbomb header make any noticeable power with the stock silencer? ive got a 98 yz400 and i wanted to get one mainly so i didnt have to loosen it when changing the oil/filter. heheh..i know im a lazy fool!. but i really wasnt looking to get a power increase that was huge. my friend has the header on his 426 and it feels a lot more snappy compared to mine, but it might be like apples and oranges. his jetting didnt change either. nor do you have to move it to get to the oil filter.