03 WR450 engine in Road Race bike Qs?

I have a 03 WR450 engine in my 96 TZ250 chassis. The bike is a blast to ride but I'm having difficulty with jetting. The guy before me ran just a screen without any filter. I don't feel comfortable with that so I put a uni pod filter on it. Here is where the bike currently is:

main: 180

starter: 85

leak jet: 70

pilot jet: 45

needle: 4th clip

idle circuit: 1/2 turn

gray wire cut

no throttle stop

It had a 200 main when I got it. It wasn't great. I've been running a 190 but the bike studders at high RPM. It seems a lot better up top with the uni filter and the 180 jet, but it backfires quite a bit on deceleration. I've looked through the jetting d-base but I don't see anyone eliminating the airbox...looks like everyone modifies it. Since I was starting with no air filter and going to an airfilter, I didn't see a good fit. Mostly, I need to gain some insight from everyone so I can better understand the carb.

Here are my questions:

1) Does the airbox mod flow as much air as a uni filter would?

2) What does the starter jet do? I've never seen one in a carb before.

3) I don't have the off idle stumble but my leak jet is way larger than what I saw in the jetting dbase. I'm confused about that?

4) Due to the high RPM stumble, I was short shifting the bike everywhere. Does this bike have a Rev limit? Does it feel the same as any standard rev limiter?

5) The bike does not hold a good idle since putting the filter on. It idled great without it, but now doesn't. The 1/2 turn on the idle screw didn't make sense to me as most of the jetting d-base guys were in the 1&1/2 to 2 turn out range. The bike idles high and slowly returns to a lower idle...everytime coming off throttle. Any ideas?

Any other tips/advice would be greatly appreciated.

Thanks in advance for any help you provide. I'm a rookie at thumpers and I've been on the injected 4 cylinders so long that I've forgotten everything I used to know about carbs.



No jetting expert here, but 180 for the main jet sounds to me excessive.

Check out this good thread that pretty much answers all your questions:


BTW: TZ's are realy cool GP race bikes! Can you post a picture of it with the WR engine in the frame?

Thanks for the link...good info. Can you tell me how to post photos? I have a couple...the engine is sorta shoe horned in but it fits. The bike is 230 lbs and makes 51hp. Very fun road racing platform. When running right on VP, I can almost stay in the draft of a stock SV650.

Pretty neat bike. 96 TZ250 w/ 03 WR450 engine and 06 R1 front end. Dukes mixture to say the least.


Definitely post some pics. Here is how to do it:


You basically open up an account with one of the hosting sites. Then you copy and paste the "IMG" link to your Thumper Talk thread or post. I would sign up for Photobucket. I was able to post pics on a few different sites. Very reliable. If your a member of any TZ groups you will probably be able to post pictures there too, using Photobucket.

. Very fun road racing platform. When running right on VP, I can almost stay in the draft of a stock SV650.


There are many upgrades available to make it go even faster. High comp piston, yz cams, etc. Just look around the forum.

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