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gunship426

yz 426 jetting?

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hello all my yzers, i have a 2002 yz426. i have put a fmf power bomb on with a fmf Q. i mostly ride between 1500 and 4000 feet in California. Ive been fighting the jetting forever it seems. right now i have a 42pilot stock needle 2nd from top and a 168main. now it feel good on top and mid but if i crack the throttle it will almost stall. if i roll it on smooth it dose OK. can you all help me? :applause:

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Go to the FMF website and go to the tech center and it will help you out with the jetting. I would put your needle to the 3rd or 4th notch. A 168 main should be OK.

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Jetting Information

Main Jet: 165-168

Pilot Jet: 42

Needle: STOCK

Needle Position: 4TH

Power Jet: N/A

Air Screw: N/A

Fuel Screw: 2.5

Comments:

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I ride about the same elevation in CA, and have been happy with 165 main, 2 to 2.25 turns on the fuel screw, everything else stock. oh yea, '02 YZ 426, full FMF Ti-4 system w/ Powerbomb.

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I have had very good results with my 02 YZ426 at the same elevations using a J.D. jetting kit. Here are the best settings I found with standard needles:

Main: 165 for 80-100 degrees or 168 for 40-80 degrees

Pilot: 42

Needle: STOCK

Needle Position: 4TH

Fuel Screw: 1.5-1.75 turns out

Good Luck :applause:

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Have any of you done the BK mod yet? STop what you are doing and do that first. The AP squirt duration was way off on the 426s.

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I have a 2000 w/ a PB header and 'Q' exhaust and I do most of my riding in the SoCal high desert (cal city, jawbone.....). My current setup is:

-168MJ

-42PJ

-OBEJP needle #3 slot

-1 3/4 to 2 1/2 turns depending on conditions

-and one of the optional AP diaphrams from an 03' 450 (cant remember the p/n though). The diaphram was in place of the bk mod as it accomplishes the same thing, just no drilling.

My bike runs fantastic. No bog, no hesitation, no detonation and minimal popping on decel.

I also have a 2mm bore and the 450 cam, so results may vary.

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I ride about the same elevation in CA, and have been happy with 165 main, 2 to 2.25 turns on the fuel screw, everything else stock. oh yea, '02 YZ 426, full FMF Ti-4 system w/ Powerbomb.

with the powerbomb header, how close does it come to your coolant hoses ?? Any issues with it melting/burning the hoses, or is it not an issue ?

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try the BK mod-or at least check yours before you get to carried away with the jetting.

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with the powerbomb header, how close does it come to your coolant hoses ?? Any issues with it melting/burning the hoses, or is it not an issue ?

Any help or suggestions would be greatly appreciated :crazy:

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It sounds like you have an accelerator pump issue, alright, and not a jetting problem. One thing you should not overlook is the possibility that dirt may have collected around the pump shaft and may be interfereing with the operation of the pump. Once you get in there, look into the pump timing, and try the BK Mod out.

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