426 Pilot Screw Problem?

Hey Guys,

Okay, so I finally have the jetting right on my bike and it seems to be running nicely. I have a 2001 YZ426F and here is what I ended up with..

Pilot: 42

Main: 165

Needle: Dynojet 2nd Clip

Fuel Screw: 3.5 Turns Out (Aftermarket screw)

Performance:

Dr D Full Exhaust

Uni Filter No Lid

Location: Phx, AZ

Alt: 1200 Ft

Temp: 60 to 110 F (Very Dry)

The issue I'm having now is the fuel screw is obviously backed out a little too much for comfort at 3.5 turns. I tried going to a 45 but had tons of popping on decel and the bike had a weird 0 to 1/8 throttle response. I wanted to know everyones opinion on this...Is 3.5 turns out too much? Should I try the 45 pilot again? Any info on going from a 42 to a 45 would be great..I tried 3 turns out but the bike pops on decel too much and 3.5 is just right. (A pop here and there). I really just don't want to lose my fuel screw from vibration...

Thanks

Yeah I've always heard that anything over 2.5 turns is time to step up to the next size pilot jet. How many turns out did you try on the 45? I would put the 45 in and start at 1 turn out and go from there. Make sure it's fully warmed up when adjusting.

The pilot is too small, as indicated by the adjusted position of the screw. If your 45 acted lean by backfiring on decel, you should consider the possibility that that jet is partially blocked with varnish. If you have a #79 drill bit, you can push the shank end of it through the orifice to check, or replace the jet with a new one.

The pilot is too small, as indicated by the adjusted position of the screw. If your 45 acted lean by backfiring on decel, you should consider the possibility that that jet is partially blocked with varnish. If you have a #79 drill bit, you can push the shank end of it through the orifice to check, or replace the jet with a new one.

It was a brand new jet. Ill try it again though..maybe I had some kind of leak going on causing it to pop.

Alright guys everything seems to be good now. I put the 45 pilot in. I have my pilot screw set at about 2.75 turns out. (Little better than before) I got it started at 2 turns out but it was idling poorly and popping alot so I gave it a few turns and some rides around the block. 2.75 was about the perfect stopping point. The bike now has a strong idle and a some pops on decel which isnt a big deal. Thanks!

Sounds about right, but at 2.75 out, a 48 might be better. Then again, if it's still pretty chilly out, you might be just as well off to leave the 45, as it will want to be leaned out a little as the weather warms up.

Sounds about right, but at 2.75 out, a 48 might be better. Then again, if it's still pretty chilly out, you might be just as well off to leave the 45, as it will want to be leaned out a little as the weather warms up.

The only thing I noticed is about 4 to 6 seconds after I turn the bike off..It makes a "woosh" sound like a very deep backfire or something. Is this bad??

Occasionally, or always?

Ever since I switched to the 45 it does it almost every time

I suppose it would help if my carb boots werent loose. :lol: It no longer makes the sound and the 45 pilot is working perfect. :thumbsup:

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