Jump to content
Sign in to follow this  

help getting new bike to run good

Recommended Posts

Hi, I have recently purchased a new 2004 wr250f. I have put an aftermarket pipe on it, removed the air box baffle, and cut the throtle stop. It seems to have pretty good power but I would like to get more low end out of it. What do you guys suggest? Also, when I give it alot of throtle from no throtle it bogs hard and dies if I do not let up. The other thing that it does is when I am cruzing at just about any speed and r.p.m. the engine does not run smooth it kind of cuts out or stutters. I do not know anything about how to tune a bike, and would really like to lean instead of just taking it to the shop and saying fix it. I have been reading alot on this forum and the f.a.q area and freemods and am getting confussed and overwhelmed. expecialy about adjusting the carb with all the talk about needles, jets accelerator pump, Please help me with some of this. Where do I start. Thanks.

Share this post


Link to post
Share on other sites

does the bike lag when its cold only?

does the throttle lag when its in neutral and you give it a hard rev?

if you want more takeoff smaller sprocket maybe

the JD jet kit sounds good

Share this post


Link to post
Share on other sites

Start by adjusting the fuel screw (pilot screw in the manual) right. It's in the bottom of the carb. Lightly screw it all the way in and then back it out to 2 turns as a baseline and go from there.

Count the turns when you seat it just so you know where it was set from the factory.

Changing the jets in these bikes is pretty easy, and you more than likely will need to do it. Here are some links that helped me the first time I did it. Now I feel totally comfortable after having done it a few times.

http://www.eskimo.com/~daddog/jetting/thepilotjet.htm

There are links at the bottom of that page for the main jet and needle jet as well. That carb is off a yfz450, but its the same carb as on our bikes and the info is correct.

Here's one on the pilot fuel screw and how to set it...

http://www.atlanticmx.com/archives/00000135.shtml

Wr450 tips and secrets (free mods etc.)...

http://www.off-road.com/dirtbike/projects/wr450f/2003_04/runright.html

That will get you started. :cry:

Share this post


Link to post
Share on other sites

Here is a basic theory of operation on the carb. Note that there are three primary throttle positions to adjust, and they overlap some at each end. The same diagram is in your manual. (You won't be able to adjust the throttle valve cutaway.)

http://www.motocross.com/motoprof/moto/mcycle/carb101/carb101.html

Get familiar with this and jetting issues should become a little more clear.

As for your current problem, I had a similar condition when I bought my 03WR. It wouldn't run steady when cruising at steady throttle settings. I was able to fix this problem by going to a 42 pilot jet from the stock 40. This is because I adjusted the fuel screw outwards (as mentioned above), and it got better, but didn't really clear up. I found (by reading here) that if you get more than three turns out from the seated position, then move up one step on the pilot jet, and try again with the fuel screw.

You should also buy a Zip-Ty or similar fuel screw (pilot screw in the manual). This allows you to adjust your fuel screw by hand at any time. I adjust mine nearly every time I ride due to changing weather conditions. The faq ( www.thumperfaq.com ) has a nice write up on how to adjust it by ear. You should practice this. Over time it gives you a feel for how the bike should run.

To fix the bog, first you have to get the rest of your jetting just right, which will take some experimenting. When you get it jetted right, if it still bogs, then read the section on leak jets in the faq. Also search this forum for 'bog', 'leak jet' and 'AP'. AP standing for accelerator pump.

The MAIN things are to:

1) Take your time.

2) Write down everything you do

3) Make only one change at a time

4) Test each change witht the bike warmed up and under load, never on the stand.

If you get stuck, ask here or on the jetting forum. :cry:

Share this post


Link to post
Share on other sites

:cry: It seems to run the same after 15 minutes , ran pefect b4 afer only 5 :cry:

Probably explained by a change in temperature or humidity. If it got colder and now runs badly, then you're probably a little rich. Try adjusting the fuel screw inward in 1/4 turn increments.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

Sign in to follow this  

×