426 jetting

As I have my engine in bits, i figure its a good time to crank up the cam timing to yz spec. From what i've read here it seems that the YZ needle is the go. My bike has a aftermarket exhaust (pretty loud) and I ride at sea level at about 25-30 deg Celcius. If anyone else is in similar circumstances, could you give me a rough idea of where to start with the jetting? The fewer times I have to remove that carb the better :) On the subject, is there an 'easy' way to get the carb in and out...any tricks I should know about?

thanks in advance


Well I can sort of start you in the right direction. First, Yes the carb can be rotated out if you loosen the inlet and exhaust boots. Not to big of a deal.

Now, my WR has YZ timing it has a stock needle. I run a 175, 42 and 3rd from the the clip. It runs very well at sea level. Oh I have the ACV mod as well. About 2 1/2 turns out on the fuel screw. After market FMF Q pipe and header as well.

Good luck. Tom

I haven't ridden at sea level, but until somebody w/ an E-taper needle who does comes along I'll suggest this as what would be a strong starting point I would think:

EKN # 5 (Yamaha PN: 5JG-14916-EN)

45 Pilot

168 main (the stock 165 may work just as well)

100 Pilot Air Jet (this is stock YZ size, PN: 7A9-14943-27-00)

Set fuel screw to conditions.

Getting the carb on/off:

There are two schools of thought on what to do w/ the carb, leave it in the boot and twist it to get at the top (needle changes) or bowl (other changes). If you want to change the Air Jet(s), and I think you do, you need to remove the carb and intake bell.

As for the throttle cables some leave them on the carb and a) create enough slack in the cables so you can work on the carb as it dangles :) remove and reattach the cables with the carb out of the boot and intake. I always removed the cables first, w/ the carb still in the intake, this requires a bit more dexterity.

So the "cables on" is probably easier.

With both intake and airboot clamps loose, and the TPS and fuel line disconnected, grab the air boot w/ both hands, right hand just above and left just below the air boot, and pull the boot away from the carb. The boot will either come off the carb or pull the carb out of the intake.

Hope this helps.

See my sig. for the jetting I am using. I run about 2K feet to 3.5K feet. For sea level, you might want to go to a little higher main, ie. 165. I use the EKP needle at setting 3. Setting 4 gives me a little bog that I do not like. I get really good power with these overall settings. :)

Check my sig, runs like a raped ape. Keep in mind I do have the home made power now which increases velocity therefore you can lean the pilot out some. JD kit is a ripper investment, you wouldnt be sorry.

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