Here's What My Piston Looks Like Jetting Question?

On my 2000 YZ 250 I'm building I'm doing a complete bottom and topend replacement! Iv read some stuff about something being lean if you rev it at I'd and it takes a couple of seconds for it to come back down! Question is that I think the piston looks like the jetting is great and I should mess to much with it but I would like to fix the hanging rev. I'm new to jetting and have done a little research but I'm not a pro. The bike has a quiet core silencer and boysen carbon fiber reeds with a fmf gnarly pipe. I'm running 93 octane gas and klotz 32:1 I live in Indiana question is what should my jetting setting be?

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keep doin what yur doin cause thats a nice burn pattern but gotta c what the side of piston look like. pull yur exhaust pipe and look at the piston thru the flange. give us a picture of that.

oh and yur running a tad rich if yur rev is hanging

Nope. If your idle hangs when you chop the throttle that rpm range is lean. If your running wot throttle then the main is lean but spark plug/combustion color is colored by all of your riding even idling.

Don't try to jet the bike by this.

if your idle is hanging you are LEAN on your pilot circuit not rich. turn your air screw in 1/4 turn @ a time until it stops hanging. if you go to .5 turns out and still have the hang you need to go up one on your pilot and start the process over. your piston looks great BTW.

That's a touch rich, but should last a long time. Ideally you want the whole piston crown black with just a touch of silver by the intake ports.

if your idle is hanging you are LEAN on your pilot circuit not rich. turn your air screw in 1/4 turn @ a time until it stops hanging. if you go to .5 turns out and still have the hang you need to go up one on your pilot and start the process over. your piston looks great BTW.

+1, could also be somewhat lean at the transition to the jet needle, which has to do with the slide cutaway. But hanging revs after you let off, assuming you don't have a sticking slide, is a classic sign of lean. Could be as simple as Jetting, or partially plugged idle circuit passages/jets, or even a slight vacuum leak, which would show up as this lean condition, but exaggerated when chopping the throttle at higher RPMs (high RPMs + closed throttle= high vacuum) But before I reinvented the wheel, I'd check the idle circuit passages and the simple checks for vacuum leaks like using a propane torch (not lit) while the engine is running at the reed cage and any other possible leak areas. Then worry about the jetting. Never cure the symptom, just the problem.

Good luck!

Definitely a touch rich, do a plug chop if you are serious about figuring out your jetting.

The side of the piston looks brand new still?

If the idle hangs after you drop down from higher rpm the air screw is not the way to adjust it. The rpm you are running in is lean and causing the surging idle. Give it a few seconds to cool off and the normal idle will return.

Fix the problem area not the pilot/air screw.

if youre trying to use piston wash to determine jetting by looking at that picture, then you are pretty damn rich by that pic.

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good example of "perfect" piston wash. id much rather just do a proper plug chop...

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