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d2cycles

03 WR450 engine in Road Race bike Qs?

4 posts in this topic

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.

Thanks,

Dean

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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.

Dean

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

http://www.thumpertalk.com/forum/showthread.php?t=454005

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.

Dean

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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