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wvbob

jetting

13 posts in this topic

99 wr400 jetting help

i bought a 99 wr400 have changed throttle stop,opened up airbox,put on a stock yz pipe.all jetting is stock.i ride 500-1500 ft, 60-80 temp.need jetting suggestions.

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this is first bike in 25 years, very first 4 stroke. could really use some jetting help.

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Well, to start with, how is it running now after your mods?

Does it pop and backfire when you decelerate?

Does it bog down when you accelerate?

Have you pulled the plug and inspected the color of it?

Adjusted the fuel screw?

A little more info and we can probably come up with some suggestions. :thumbsup:

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no backfiring or popping on acceration, no bog,have noticed slight popping on deceleration.sometimes have to use choke even when hot.fuel screw adjustment does not seem to change anything.plug looks ok.45 pilot jet, fuel screw 2 turns out,stock needle 4th slot,172 main jet.seems to run good with mods, but being new to this bike i am not sure how it should run,thanks.

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my BEST advice is to buy yourself the JD Jetting kit. Many of us have, and are COMPLETELY happy. I spent mucho $$$ and YEARS working on my jetting. I have a buttload of needles and main jets to prove it!!

FACT: Thumpertalk was conceived on the lack of knowledge of the carb on the 98/99 WR400 >> this IS absolutely true!!

JD (James Dean) was one of OUR carb guru engineers working out the jetting issues of his 99 WR.

After MUCH R&D, he has designed his own custom cut needles. His kit somes w/ two needles and several main jets AND instructions to jet properly.

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From your descriptions, it sounds like you have it dialed in pretty well. If it runs just like you say, I wouldn't change a thing.

It is fast right?

Oh and if you feel like investing the money for it, they say the JD kit is night and day over the stock stuff...

For my needs I think the cheaper stuff will work fine. I don't race it.

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found out why fuel screw makes no differance.the tip of the screw is broke off blocking the passage shut. anyone know how to get this out? it is stuck solid. thanks.

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i tried compressed air, also tried a wire, that did not work either. may need a new carb?

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You should give the folks over at Zip Ty Racing a call. I remember a post from someone that broke their ZipTy screw and they were able to get out the broken piece. Maybe they can help you.

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zip ty racing did remove the broken fuel screw and replaced it with a new one -no charge!

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