WR450 YZ Exhaust - Jetting ??

1 reply to this topic
  • bg10459

Posted June 16, 2005 - 12:00 PM


OK, I bought a used 03 WR450 with cut grey wire and shortened throttle stop. The guy I got it from said he had it jetted, but it came with the intake snorkle and exhaust restrictor in place. I didn't ride it until after I removed the intake snorkle and the exhaust restrictor. Everything seemed OK except a slight miss at WOT in high gear. That was a colder weekend, about 45 to 55 degrees at 1200' elevation.
Then I went riding again, maybe a 75 to 85 degree day at 2000' elevation. Everything seemed the same, but maybe the high end miss was slightly worse (maybe I'm just getting better and riding harder now :) ).
Now I just changed to a YZ exhaust. Just a short blast down the block, but the high end miss was a lot worse, again maybe 75 to 85 degrees at sea level. Maybe it wasn't fully warmed up.

Anyway, my questions are:
1. Is the YZ exhaust so much less restictive than the stock, uncorked WR exhaust that it would cause the high end miss to get dramatically worse?
2. Is the YZ head pipe the same as the WR headpipe?
3. I assume I need to change the main jet to address the problem, but which way? Bigger or smaller?
4. Hard starting with the E-start when warm, kicks easy. What to do?

I have yet to take the carb apart, so I don't know what's in there, but I just got my JD Kit and fuel screw, so I plan on re-jetting anyway. Most of my riding will be between sea level and 4000' and normally on warmer days, 65 to 100 degrees, humid northeast. I suppose I could just follow the jetting recommendations in the d-base, but I'd rather not make too many changes at once.

Thanks in advance.

03 WR450f
92 WXE360
86 CR250

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • bg10459

Posted June 21, 2005 - 08:08 PM


OK. Now I've got some info to throw around. Here is what I found:
Needle - OBEKP #5 (YZ Needle??)
Main Jet - 145
Pilot Jet - 45
Pilot Air Jet - 70
Starter Jet - 65
Leak Jet - 70
Fuel Screw - 1.5 turns out
YZ Exhaust
Cut Grey Wire
Intake Snorkel Removed
Throttle stop cut (way too short)

I'll put the YZ throttle stop in first. Could that have had anything to do with the WOT miss? The 145 main may have been drilled because it looks bigger than the 170 that came with my JD kit. I put in the Zip-Ty fuel screw at 1.5 turns out and I was planning on just changing the main to 160, but while the carb is out... maybe I should follow the D-Base recommendations and change the needle too??? I didn't want to make too many changes at once though.

Can anyone help me?

Anyone? Please!


Join Our Community!

Even if you don't want to post, registered members get access to tools that make finding & following the good stuff easier.

If you enjoyed reading about "" here in the ThumperTalk archive, you'll LOVE our community. Come join ThumperTalk today!

The views and opinions expressed on this page are strictly those of the author, and have not been reviewed or approved by ThumperTalk.