WR stumbles on top end!

Sorry to fool you on the title, But its a WR250F im questioning about.:D

I know theirs alot of smart guys out their and am hoping to get some exposure on this to someone experianced. So please bear with me and read on.......

The bike is a WR250F-2007 Its mods= Exhaust restrictor removed, air box snorkel removed, Boyseen accel pump and jetted accordingly(not by me but a professional)

History= The bike has not been abused, ran mint when I bought it and for several tanks of gas and has been well maintained.

The problem= One day out of the blue, it started to stumble on the topend like it was hitting the rev limiter when it was not. The bottom and mid ran and still runs mint(nearly 2 months later) The plug comes out sooty black. The first thing I did was change the plug, dump the gas and get new gas, check the choke to see if it was seating properly and checked for junk in the carb bowl. Still crap. I took it to the gut I bought it from(has a shop) and he tore apart the carb and started to re-jet it.(BTW their was no siginifant change in temp) I went to test ride it twice and the jetting changes did change the upper power band but not in a manner that fixed it. He ended up going so lean that he was several sized leaner than stock. When I test rode it, it did start to pull through the upper powerband but lacked its "hit" Definately not fixed, just masked. He could not find any other problems and relieved himself of working on it anymore.

I then took it to another guy I know that only works on Motorcycles that is the best around I know of. He started by tearing apart the Carb and found nothing wrong, clean as a whistle. He agreed what was done earlier was not a fix but a mask of the real problem. He then went to the electrical. Tested the coil, T.P.S and everything he knew of. The end resault was that it needed a new CDI box. I ordered a CDI which is a elec- non-refundable/returnable part($197). Put it on tonight with a new clean air filter and...... no fix!!!!!!!:worthy::busted::blah: W.T.F????????

I have no idea what to do next except the dealership which I doubt their smarter than this guy(Ive known him for 8 years+, he makes dealerships look like girlscouts)

Last peice of info= Once again it runs mint on the bottom and mid. It is DEFENATELY not the carb. The plug is always black. When I twist the throttle up to 1/2 to 2/3 and hold it, it revs out smoothly and will go fast-70+mph. When Im going 1/2 to 2/3 throttle and suddenly twist it W.O. it studders, not bogs but studders.

Any help guys? good, bad or ugly welcome!

Thanks for any replies that may resault form this being posted in the wrong forum :thumbsup: Jason.

After reading the first couple sentences I thought it was a bad CDI but reading further, you've ruled that out......I still bet its something electrical......wish I knew more and could help you out......will follow this thread to see what solves the problem.

I'd try going the other way, richer, on the main jet. Mine did the exact same thing.

I'd try going the other way, richer, on the main jet. Mine did the exact same thing.

Richer on the main jet? The plug already comes out black and sooty. This will happen on a new plug in about 2-min of run time.

The plug already comes out black and sooty. This will happen on a new plug in about 2-min of run time.

Hmmmm, does sound rich. I also just noticed that you are refering to a 250...sorry I can't read, I was thinking 450.

More than likely the soot your seeing is caused from the accelerator pump dumping too much gas in the cylinder, it could still be lean at 3/4 to wide open. The AP is so darn finicky......another thing to check is the TPS using an ohm meter.

I bet he's running the blue needle:lol: :thumbsup:

I bet he's running the blue needle:lol: :worthy:

Ouch!:thumbsup:

I have a friend with a Husky that this happened to also. Fine up to 3/4 throttle and then a stutter as it wouldn't rev out.

In the end the problem was a short on one of the wires. Not sure which one as he had it fixed at the shop and is not mechanically inclined.

have you checked for cracks in the spark plug wire? My friend had a similar problem with his 2004 WR450. Once he got to a higher RPM his bike would studder because the spark plug wire was cracked and it would start arcing to the motor. I think the vibration at a higher RPM would cause the crack to open just enough to arc. We electrical taped the wire and no more troubles.

Adam

More than likely the soot your seeing is caused from the accelerator pump dumping too much gas in the cylinder, it could still be lean at 3/4 to wide open. The AP is so darn finicky......another thing to check is the TPS using an ohm meter.

Tps sensor was checked by a mechanic. OHM'd perfect. I suppose nothing is perfect in the real world though?!

I have a friend with a Husky that this happened to also. Fine up to 3/4 throttle and then a stutter as it wouldn't rev out.

In the end the problem was a short on one of the wires. Not sure which one as he had it fixed at the shop and is not mechanically inclined.

Dosnt seem to be as much RPM related as throttle opening related. At 3/4 throttle is will rev smoothly through the range. At 100% throttle opening is when it stumbles or under a load.

have you checked for cracks in the spark plug wire? My friend had a similar problem with his 2004 WR450. Once he got to a higher RPM his bike would studder because the spark plug wire was cracked and it would start arcing to the motor. I think the vibration at a higher RPM would cause the crack to open just enough to arc. We electrical taped the wire and no more troubles.

Adam

Good suggestion, thanks. I will check that tomorrow. Sounds like its time to start looking at all the wiring.

Ive been told to check the grounds. Where do I start?

Last peice of info= Once again it runs mint on the bottom and mid. It is DEFENATELY not the carb. The plug is always black. When I twist the throttle up to 1/2 to 2/3 and hold it, it revs out smoothly and will go fast-70+mph. When Im going 1/2 to 2/3 throttle and suddenly twist it W.O. it studders, not bogs but studders.

Any help guys? good, bad or ugly welcome!

Thanks for any replies that may resault form this being posted in the wrong forum :thumbsup: Jason.

Aaaaaaaaaaarrrrrrrrrrrrrggggggghhhhh!!!!!

A blackened plug is a vital clue!

Why on earth are you screwing around with the electricals!!!!

The bike is getting TOO MUCH FUEL!! Plain and simple.

Before you spend any more money on quack mechanics check the basics;

Are the carb vent lines plugged with mud?

Is the float level set correctly (more on this in a moment)?

Air filter is clean and NOT OVER OILED?

Is there any fuel coming out of the vent lines while the bike is sitting and rinning at idle?

My bet is that you have more than one issue WITH THE CARB.

The float level being wrong (set too high) is probably a contributing factor but not the only problem. Only one in every five FCR carbs I've had to work on has had the float level set correctly. The spec that Yamaha uses is 8mm. The Keihin spec for FCR float level is 9mm. The 8mm setting that Yamaha uses makes the bike run rich and difficult to jet correctly.

Set the float level to 9mm.

The breaking up at high rpm's is most likely due to a main jet being too big.

Aaaaaaaaaaarrrrrrrrrrrrrggggggghhhhh!!!!!

A blackened plug is a vital clue!

Why on earth are you screwing around with the electricals!!!!

The bike is getting TOO MUCH FUEL!! Plain and simple.

Before you spend any more money on quack mechanics check the basics;

Are the carb vent lines plugged with mud?

Is the float level set correctly (more on this in a moment)?

Air filter is clean and NOT OVER OILED?

Is there any fuel coming out of the vent lines while the bike is sitting and rinning at idle?

My bet is that you have more than one issue WITH THE CARB.

The float level being wrong (set too high) is probably a contributing factor but not the only problem. Only one in every five FCR carbs I've had to work on has had the float level set correctly. The spec that Yamaha uses is 8mm. The Keihin spec for FCR float level is 9mm. The 8mm setting that Yamaha uses makes the bike run rich and difficult to jet correctly.

Set the float level to 9mm.

The breaking up at high rpm's is most likely due to a main jet being too big.

No mudd in the vent lines

Float level checked at 8mm(will try 9mm)

Air filter perfect- cleaned and not over oiled

No fuel coming out of the lines while idling

1- The problem occured overnight. I rode on a friday and- perfect. The next saturday morning- crap. Mudd in the carb vents I can understand, but the float level changing drastically how it runs overnight, Im not so sure.

2- If it was loosing partial spark at WOT, wouldent that also blacken the plug? Not properly combusting the mixture, but still dumping in fuel?

3- It will rev out smoothly, just not at WOT. If the throttle is at 3/4, I can get 70 mph out of it smoothly. If the throttle is at WO, cant get much. With that said, is sounds like the main jet. The reason were convinced its not= Before the problem occured, the powerband had a little "hit". After the problem, the jetting was the first to be messed with. When they got it to rev out smoothly at WOT, I test rode it. Yes it reved out, but the "hit" was completely gone, and they had the main jet substantially leaner than stock with the plug still coming out slightly black. The bikes exhaust restrictor has been removed, snorkel removed, and it has a Boyseen Quickshot2. With these mods the main should be and were(when it ran good) richer than stock. Seems clear to me that they were masking the problem and not fixing it.

This thread seems to have died a death without good reason.

Jason - We'd be interested if you found a solution! Was it electrical? fuel-related?

Cheers mate

This thread seems to have died a death without good reason.

Jason - We'd be interested if you found a solution! Was it electrical? fuel-related?

Cheers mate

Yes please tell us what happend I am having the same issue on my 03 450:banghead:

Stutter = rich. Bog = lean.

Simple.

Stutter = rich. Bog = lean.

Simple.

Negative it has nothing to do with the jets trust me

Accelerator pump out of adjustment?

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