01 yzf426 w/ fmf Q jetting or tuning help?

Hello John,

I never had the bog with the white brothers E series exhaust which had 18 disks. As soon as I put the FMF Q on the bike started to bog on the bottom end and run real rich. I have purchased a 40 pilot and may try to move the needle down but just haven't had a chance to try it yet. I may look into these other mods if I can't get the bog out this way. Thanks for the info.


Hello again Brandon V,

By the way, nice name. How much did the 450 diaphram run you ? I have been recomended to try the 40 pilot over the stock 42 and then move the needle to see what happens. As soon as I get a chance to ride the dam thing I will know if I need the diaphram or any other carb mods. It ran great until I put that FMF Q on and now it runs like crap. Are you running a FMF Q on your bike?

Brandon M.

Nice name yourself :cry: There's a few Brandon's arouns here now, we're taking over!

I've got a DSP titanium exhaust which is less restrictive than the Q as its a closed course exhaust. Also, I can verify that I run a #40PJ, 158 main, OBEJP needle in the #3 pos. and 1.5 - 2 turns on the screw depending on alt. The bike runs like a raped ape....

If you feel like making the trek to the Gorman/Frasier Park area next time we go you're more than welcome to ride it, plus you can try out the 14/50 gear combo :cry:

The 450 diaphram is around $10-15, cant remember exactly but I felt it was worth not having to drill & tap a screw into the carb.

I'm off to Vegas, please let us know how it goes so I can see when I get back. Later!

So what happened?!?!?!

Brandon M, if you are in Paso go see Huft Daddy at Powerhouse. He can set you up with the different accelerator pump diaphrams. It's not just a YZ450 thing, but is also available for your 426. Yamaha simply sells optional parts for the diaphams; leaner to richer.

I doubt the accelerator pump is your problem. I'd start with the pilot jet and work if from there.

Also, the position of the needle will give you a bog too if not in the correct position.

I would bet (although :cry: not to much) its the needle!Let us know what you find out!

I am planning to try some of these tips out on Friday and Saturday. All my family will be leaving by then (thank god). Hopefully the rain lets up so I can ride the thing this weekend. I will post my results.


Hello everyone,

I just wanted to thank you all for the help with my sick bike. I cleaned out the carb with carb cleaner, installed the 40 pilot jet , dropped the needle down one notch (#3), installed the 03 YZ450 accelerator pump diaphram, and topped it off with the ZIP/TY adjustable fuel screw set at 1 and 1/2 turns out. This thing is so crisp and responsive now! I also dropped my gearing back to stock and it's like ridding a different bike that is way more responsive from idle all the way to wide open throttle. Nice cheap power improvement without the guesswork. Thank's again,

Brandon and a happy 01 YZ426

Nice dude :cry:

Those tweaks made a world of difference on my bike too. I know there's a few more ponies I can squeeze out of there with some more tuning, but I've been wanting to ride more than tune lately. Give me a shout if you ever want to ride down here..... Los Padres Nat'l Forrest is only about 2 hrs from you.

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