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Octanee

i think my 426 needs rejetting... help me out with how!

10 posts in this topic

hi guys, got a 426 here and basically cold it will fire up pretty darn good, i just rebuilt the sucker, high comp piston, i think its 13.5:1, replaced all valves, did auto decomp mod it idles and runs strong, however when you let off the gas, it does not pop at all, my 06 yz450f pops.... also this bike has a twinair filter,

so basically heres my problem, the big one, when its hot and you want to start it.... good luck, hot start does not help, you know what does? CHOKE! if i put the choke on then the sucker starts right up... so thats not right, now is it?

my 06 450 i dont need hot start or choke i can just give er a kick and she fires up, so i'd say my 450 is properly jetted, so i havent had to touch my carb,

and so i dont know how to adjust these carbs on these bikes and how i should go about it?

so what would you guys recommend me to touch on the carb first? since it wont start hot unless you use choke to get it going and it does not backfire at all when downshifting, must mean its really rich? or more like lean possibly?, Thanks!

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It is too lean on the pilot jet and/or fuel screw. Typically these bikes run best with a 45-48 pilot, sometimes even a 50, with needle around 4th clip, and a 175ish main jet. Search around on how to tune the pilot circuit and you should be pretty much all set. Not exactly what effect the high comp piston will have on jetting so you may be slightly different from what I just typed.

Edited by Pooley

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mine came with stock 42 pilot and a 165 main.I had to drop the pilot to a 40 to get it to run right.I used to have to use hotstart all the time when hot and it would stumble at low rpm riding.40 pilot made her run awesome and haven't used the hotstart after to get her running.During no throttle coasting there it is a lil bit of popping.

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ok good to know for a base line, the 42 pilot or a 40, is lower number = richer or leaner? and needle position, down deeper in hole = leaner and higher = richer correct?

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40 would be leaner and further down the needle sits is leaner.

ok well im going to assume, that if it needs choke, which = more fuel to start while hot, that it probably needs more fuel as in it runs too lean right now? would that be a good assumption? Thanks!

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Sorry, I should have been a little bit more accurate in posting some of those jet numbers. Those are for near sea level (I'm in Michigan at about 700ft above sea level), with all free mods done and a performance exhaust. Also, I ride the WR but I have my bike exactly the same as a YZ in terms of carb and jetting. I found that I was way too lean with stock jetting after all the modifications to make this thing run properly.

Edited by Pooley

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Sorry, I should have been a little bit more accurate in posting some of those jet numbers. Those are for near sea level (I'm in Michigan at about 700ft above sea level), with all free mods done and a performance exhaust. Also, I ride the WR but I have my bike exactly the same as a YZ in terms of carb and jetting. I found that I was way too lean with stock jetting after all the modifications to make this thing run properly.

alrighty, so my best bet to start, if i think i need to Richen it up, is to lift my needle inside the carb i take it,

and grayracer thanks for the links as always!

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If you are having trouble with starting, start with the pilot jet/fuel screw. Once that circuit is fixed, you can move on to the needle and main. There is a stickied post that explains how to properly tune the pilot circuit. Give that a read and see how things turn out.

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