Should I try to Jet my WR to YZ specs ??

I have the yz exhaust cam and muffler on my bike, with all the free type mods done, removed smog kit, and jetted to the sticky thread above, but it's still not quite right, I tried to richen/lean out one jet at a time, still can't it perfect, Im wondering if I should jet her up same as the Yz as now I think im as close to the yz engine i can get without buying one. I get some black smoke build up on my liscence plate and some backfiring still on decel (yes i have boysen cover and adjustable mixture screw) so Im still rich somewhere and lean somewhere but I can't seem to narrow it down, wondered if going to the YZ jetting and plugging off that air valve on our bikes also to make the carb like Yz, what do you guys think??

What I think Mountain Max, is that that soot could be the result of the ap and nothing to worry about if your bike is running right. All race bikes and cars seem to backfire on deceleration and those things must be jetted to near perfection, something to do with the straight thru exhaust I think.


It is the ACV.

If you change to YZ specs, expect to get sharper throttle response, less roll on, and a bit more popping.

You will still get the soot as chopping the throttle still results in unburnt fuel getting dumped.

oh, ok, thanks.....

I feel your pain mountain max. I've had my carb off about a dozen times jetting and re-jetting. I got it dialed in pretty close but it's still not right. I have done all the same mods, but this carb is just too sensitive. It's like a chick, you got to mess with it too much to get it to work right :thumbsup:

Maybe in a while I'll break down and spend $400 on a new DG carb, simplify the solution.

yeah, they are picky, and I want to get mine just right, will eventually figure it out, I hate screwing with all the dam cables and hoses every time trying to get the carb off, and if i followed the manual, it would take 4 times as long.......

yeah, they are picky, and I want to get mine just right, will eventually figure it out, I hate screwing with all the dam cables and hoses every time trying to get the carb off, and if i followed the manual, it would take 4 times as long.......

Yeah, the one good thing about it is that I can remove my carb, re-jet it and re-install it in about 20 mins. now. I started another thread asking people about aftermarket carbs, I'm seriously considering it now.

Yeah, I must say I can get the carb off pretty quick now also, but it's still a pain. Next I amay try a smaller leak jet to try to get rid of my bog, and go from there.

Let us know how it works.

MountainMax, how lean have you tried on the needle position? Soot on your bike sounds like it's rich in the cruize area of the range - part throttle, light load. Did you get rid of that jerking around at part throttle completely? Still sounds like you need to raise your needle clip further or maybe need a different profile needle. The backfiring on decel also points to the possibility you are compensating for the rich needle by leaning off the pilot.

well when i put my mixture screw out about 3 turns she don't backfire on decel, so i was told to up my pilot size, im up now to a 50 and still needs 3 turns out, I tried to move the needle cip up and down also yes, dam tricky stuff.....

Hate to revisit this for those familiar but have you had your carb slide out? It can cause all sorts of problems if not put back the right way - some guys have even reported incorrect installation from the Yamaha factory - go figure.

A 50 pilot sounds too rich at 3 turns out. You did not say what your other jets were but I would go back to basics and use the chart by Clark and Indy. They are THAT CLOSE. Then change ONE thing at a time.

For what its worth I would suggest blocking the ACV once you have the MJ, needle, pilot and leak sorted. People sing the praises of a ZERO leak but NO (carb) bike will be perfectly BOG free from idle with no load. I found the ACV richened the bike and I could not get steady low throttle running. I think my ACV was cutting in and out. The TPS helped but the bike ran rougher. So I recommend leaving TPS unless pure road riding. I tracked it to ACV interference when high carb vacuum state. the YZ does not have ACV carb (??) so the only way to achieve close to YZ jetting (42 Pilot) is to deactivate the ACV. If you want to try go to: and gen up first-saves a lot of Qs.

The ACV supposedly prevents the popping by allowing LESS air to emulsify through the pilot circuit at closed throttle. While I cant be sure this is your problem (not all ACV springs are equal) I found that with the standard MAJ the bike was more responsive to idle and pilot circuit adjustments with the ACV blocked in the normal position - OPEN. With the ACV deactivated the bike will pop more. An extra 1/4 to 1/2 out on the screw lessens this but the bottom 1/8 to 1/4 throttle setting is a little rich then so can cause stutter, so then you are onto raising the needle clip etc etc. So, with ACV mod just accept the slight increase in POP. My .02 :thumbsup:

the rest of my jets are as indy specs already, i just tried to go up from 48 to 50 main to see if it would help, I have not had the slide out yet, but the next time i remove the carb im gonna check it out, read threads on this here b4, just never pulled it since.

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