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Another Wr450 Jetting Problem

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Hey Fella's..I have read and tried countless members settings with this bike and can't seem to win..so here is what I have done so far.

The bike; 2007 wr450

exh; FMF header, with FMF POWER CORE muffler

YAMAHA AVS removal kit and kit jetting tried

PROBLEM...part throttle 'POOTTING' (for lack of better term).And on the stand while doing the following adjustments, I have noticed a BLUE FLAME at the muffler tip and backfiring. At close of today's testing I have tried all of the following.The bike has been put on the street in full street trim.

What I have tried...JD KIT; 160 and 165 main, both red and blue needle in all positions. Tried 2007 yz 450 needle and 2007 wr450 needle and the AVS kit needle in all positions.With 160 and 165 main

I also have the ZYP TYE air screw..adjusted 2.5 and 2.0 turns.

As of today my setting are;RED #3 position, 160 main and 140 leak, 2 turns on air screw.

Just off idle I get what some would describe as a REV LIMITER effect.

Just to add about the needle positions, if I put clip into top position the engine would refuse to rev off idle..that is with all needles.

I ride mostly here in the south..Georgia, Florida and Tennessee. ave temp. around 88.

So if you have any ideas here, unload them and I will try them. I have the bike on the stand with a gas tank rigged up remote and do the needle and jet changes with min. effort.

Thanks for any input you all may have.

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First, test on the stand is pretty useless. You have to test by having a load on the engine.

To attempt to translate, you are getting a stuttering just off idle. Is this during acceleration or steady throttle?

Do you really have a 140 leak jet? Never heard of one that big.

What is a AVS? Do you mean AIS (Air Injection System) or ACV (Air Cut Valve)?

Did you set/check the fuel screw and pilot jet using the perscribed method?

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Hey William1 thanks for asking for more info. As far as the studerring goes it is under part throttle. I have done the oring trick to the accelerator pump and checked it's timing.

And I did mean AIS.

I will double check the sizing on the air bleed..but it is the one supplied with the JD kit.

As far as the air screw adjustment..I adjust till I get a smooth idle and this is where the engine seems to be the quickest off idle also.

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Unfortunately, steady throttle studdering is 'built into' the WR's. So far, the only solution appears to change the CDI to a Vortex unit, a pricey soultion. A search in the WR forums will revel a thread involving James Dean and a detailed analysis of the issue and resolution. I am currently pursuing an option that my reduce it to (I hope) an acceptable level, at least for when on the road DS'ing between trail heads. There is a thread there about putting a switch on the TPS that is ongoing.

AIS has no effect on jetting assuming you properly capped off the vacuum port on the intake side of the head.

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Can I jump in on your thread. I've got a 2003 WR450, which also has a stuttering at a steady throttle, kinda feels like a missfire sometimes or even just the pulses of the 4 stroke cycle, but definately feels like a stutter at steady throttle. Apart from this it starts well hot or cold, and drives like a demon at wide open throttle, running a 160 main, 48 pilot, 65 starter jet and 2.5 turns out on the mixture screw.

I've been searching everywhere for a thread like this and was quite interested in William 1's knowledge of the WR. I rode a 2006 model for a weekend in Spain which didn't appear to have this stutter so do believe it is possible to get mine to an acceptable level as you rightly say William. I've had a little bit of success in improving things by gearing the bike a little differently by putting a smaller rear sprocket on the rear (48) the bike seems to feels happier like this, not sure why ? Today I tried dropping the clip on the needle to run a bit richer which didn't really make any noticeable difference, I'll try leaner next.

Any advice you can give is welcome, off to read the James Dean site now and the TPS thread.

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Hey GLENWR450,

Did you ever get that missfire fixed? I have what sounds like the exact same problem. Mine is a bit variable though, sometimes it is worse than other times.

The missfire sounds like a rev limiter at low throttle, but mine is a bit RPM dependant. About 1/8 throttle and over 3000 rpm it misses bad. if i give it a lot of throttle it runs perfect, and it idles well.

I have an 08 wr450 with similar mods.

I have been getting some dirt in the float bowl.. I tried to clean the carb on the bike, removed the jets, bowl cap and air filter and sprayed a lot of carb cleaner through it. but it still has some of the issue.

Plus the problem seems to come and go, and my idle speed keeps changing about once every 3 hours or so.... I cant for the life of me figure this out.

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Hey there Diesel Junkie

To answer your question...no I have not 100% gotten rid of the part throttle studder..but with the 165 main, red needle in the second from top grove and the supplied leak jet in the JD kit, I have gotten the studder to minimum.

Like yours.. when I go to wide open throttle this studder is not there.I have not maintained a full throttle for any length of time to see if it shows up, but non the less it is faintly there now with my last jetting foray.

I still did not figure out way on the stand the bike would go right to limp mode off idle. I understand w1's comment about being loaded..but I use engine dynometers with out loads to check rev. limiters, with 2 strokes and 4 strokes and after ignition and fuel have been straitened out, I don't see this problem.

There is another thread you may want to check out under ignition here. Some of the guys, including W1 are working on an interrupt switch for the bike. Seems some one had use of a 'I' scope and found a ignition flaw for the wr450. Check it out.

Later this summer I will be able to work on the bike some more, and will post my findings.

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I have the switch all figured out. I'll admit it, I have been distracted and have not done anything. But tests done seem to confirm, it will greatly reduce the stutter. Keep in mind, this fix is simply to make transition from trail to trail easier/more pleasant. You will be down on power while the switched to 'non stutter' mode. From what I can tell, it should function on the fly though having to shut down, hit the switch and restart is no big deal.

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can't belive its been a year trying to fix my problem...so after even move carb work and cleaning I broke down and bought the Vortex X10 and a '08 yz450 carb.

First installed the X10 and tried the on stand test..while running the bike I checked the charging of the battery and found that the voltage input from idle to PROBLEM was steady at 13.8v..then when PROBLEM showed up at 3/4 throttle the volts would drop to 12.06v..hmmmmm.

There is a positive difference with the Vortex and I now belive my 'SHOOTING DUCKS' out the pipe will be directly related to the voltage drop. When I get back home next week I will try to add a charger to the testing and see if this helps or may have to try a new regulator or stator.

Installed the YZ carb and the idle and throttle response up to the PROBLEM really seemed smoother than the Tricked out WR carb. The only change I made was the 168 main.

I add the VOLT check to the testing based on info I got from MIKE TOOLE at MT Racing..he is the state side Vortex dealer. He told me that Yamaha sent out a bulletin that OVER charging would affect the regulator resulting in ignition problems. So may be I am getting closer to my fix.

Maybe all coincidence..but all this started after I tried a gas additive. Only racing gas from now on.

And just to clarify my problem is still SHOOTING and popping out the muffler..The inherent STEADY THROTTLE STUDDER is gone with the X10 installed and set on #7.

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It's been a while but I've just been living with the stutter ever since my post, kinda get used to it, until today.

I recently bought a AFR meter (air fuel ratio), I always thought I new enough about carbs and understood the principals of jetting.

Anyway after struggling to jet an FCR to a Husky WXC 410 (TE), I thought sod it I need to see what I am doing and bought the AFR meter. Good bit of kit that I can use on any bike or car.

Long story short I,ve dialled the carb in pretty well now, a little bit richer than stoichometric all round between 12.8 - 13.8 ish, the stutter has vanished, it's early days and i've only had one test ride but at steady throttle 40 mph no stutter.

I didn't get the meter for the WR, but it revealed I was running way rich, Just some info that may be of help to someone.

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