My 01wr426 Vs My 04wr450

I Sold My 01 426 A Few Days Ago And Just Got A 04 450 Home Today. Has Factory James Kit...gytr Full Exhaust...skidplate...frame Guards...msr Sucks Against My 426...???the 426 Runs Like A Scalded Ape. The 450 Barely Pulls The Front End Up When I Hammer 2nd Gear. 426 Idles Great Smooth All The Way To Topend....450 Idles Great Misses And Surges All The Way To About 3/4 Then Smooths Out To Topend...any Suggestions?????also Can Someone Give Me A 1-2-3 On How To Search Old Threads????? Thanks Guys, Yall Have Been A Great Help To Me In The Past.

has the throttle stop been changed to a YZ? that makes a hell of a difference. If thats been done I'd say it was jetted badly or something.

Never ridden a 426 so cant compare the 2, but my 450 has NO problems pulling the front end up in whatever gear I choose, so somethings up with yours

I just bought a 2001 wr426 used from a dealer in Colorado. I rode it the same day I bought it because the shop swore they changed the oil, cleaned the filter and swapped the plug. I kinda doubt they were telling the truth....but anyway it ran great in their parking lot where i could barely get out of 1st gear. Once at the track that day it seemed like it was missing and very short on power. I brushed it off and decided I was being paranoid and that it probably just needed the free mods. I made the changes and could immediately tell the difference. It had more power but it was missing in a very minor way. The changes I made were that I removed the snorkel, removed the baffle and unpluged the grey wire. It was pretty nice at about 70degrees. It ripped around the track but something just still didn't feel right. I took it for a street ride next hoping to get a better feeling. It was chilly, probably in the low 50s and it ran like complete crap. The next time i rode it was down in the 40s and it was worse. This miss just keeps getting worse. So last night I reversed all the mods, cleaned the air filter and cleaned the plug. It was much better but still had a slight miss and seems to be laking major power. Any ideas? Mine is definately no scalped ape! I wish she was though! What was your setup, mods and jetting on your 2001? I apologize for intruding on your post but would really love to hear. Thanks!

youll need to get the AIS blockoff system when its off back order from yamaha. that should help with the power delivery quite a bit.


if its a new '04 wr450, just break it in. after 200 to 300 miles, you will see a big dfferance.

Darkhorse, search this forum for LarryCo. He did an absolute ton of jetting work on the 01 WR426. My bike fouled plugs left and right and when one is going, it will run just like you are describing. I eventually bought a pneumatic plug cleaner from Harbor Freight which pays for itself very quickly.

For our altitude, you'll need to lean the bike out a lot, do the BK Mod, open the airbox and at a bare minimum install a PMB or GYRT insert. An FMF Q or similar pipe will help a lot.

My bike hauled balls. I had no problem out dragging an XR650R, KTM 525 EXC, KTM 450 EXC, etc every time.

If it's really cold out, you may need to block off part of one of the radiators. Otherwise, you'll foul plugs.

vmax - what kind of carb settings are you having good results with here in CO? I'm in the Boulder/Longmont area, and my bike was running great but has recently started fouling plugs (too rich, I think). I have not done anything to the carb. I've been running a Q silencer, stock head pipe, and White Powerfilter with airbox lid removed.

It runs fine for a while, then has this intermittent bogging in the midrange under acceleration. It starts and idles fine, and there is no backfiring. :naughty:

Do I need to raise the needle as a first step and go from there? Like I said, bike ran awesome all last summer with no carb tinkering. Maybe worth noting that this problem developed after a very, very muddy ride over in Montrose which had all my breathers plugged up and the bike ran like shit & fouled the plug. Hasn't run right since then. :naughty:

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