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'02 WR426 misfire issue

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Posted by: Strick---------------------

For those of you who might have seen this same thread on another forum, I apologize for the redundancy. I am coming back to the granddaddy to hopefully get some insight.

Here is the story:

I am a long time KTM rider. I need a second bike for numerous reasons. I have always liked the Yamaha thumpers, so I am going to buy one (I think). I have a line on a 2002 WR426 that I can get for $2500. It is in incredible condition, with extras, like O-ring, Ironman sprockets, Scott's ready, exc. It has a popping or hesitating during acceleration. It is YZ timed, has a new black box, and the carb has been gone through numerous times. A carb was also taken off of another bike that ran fine and when put on this bike it still had the popping/hesitation problem. Also - It had this problem even before the YZ timing.

Here are my series of questions:
- did the '02-WR have any reported CAM problems (mis-ground)
- Any common electrical problems
- Any Valve train issues
- A few KTMs had the bottom part of the slide installed backwards that created issues - any Yamahas have this problem.

I do not want to become a frustrated Yamaha owner after years of owning KTM's, but I have always liked them and HAVE to give it a try.

HELP!!


Posted by: biglou---------------------

The slide might be installed upside down. Very easy to do (so I've read). Something about the orientation of an "M" or something stamped on the slide is the indicator.


Posted by: JasonJ---------------------

There was an issue with the slide even cracking and breaking especially when the throttle stop was removed instead of cut. Has the gray wire been cut? If not try that too. $2500 sounds like a great deal. You might want to check the timing yourself and ceck the valve clearance since you dont know for sure if it was done right. Is the carb on it still jetted for the WR? YZ timing usally requres a re-jet along with a different needle taper.


Posted by: SFO---------------------

Strick, what kind of mileage is on this bike?
If I was to buy such a project I would consider a top end inspection to be very reasonable if my goal was to get a couple seasons of trouble free riding out of this bike.
The parts are very reasonably priced and there are many spares available on the F/S forums between here and TT.
I would say 2500 is a great # that would leave room for a tidy little freshening up of the top end. Then you can rest assured that you have no ??? in your future.
OTW, I have a tuning guru in the bay area that fixes all of my sniggly problems that myself and others can't requite.
I would say 2500$ is a # that allows room for some parts and labor, barring a broken frame or busted casses I would jump on it.
There are no real mechanical gremlins/issues/pacers, as far as I know, just be very careful tightening the cam caps.
Hope this helps.


Posted by: Strick---------------------

Carb off of another Yamaha and still the same problem - I don't think it is carburation, but I will go through it when I get it.

The bike has 3 months riding time on it and 2 races, AND I know the owner very well. I would say the bike definitely has less than 50 hours on it, and maybe half that amount.

Thanks for the replies!


Posted by: Humai---------------------

Strick, wrestling with a secret blue bike fetish, eh?

It sounds like you have discounted carburation and I would be surprised if the cams or timing chain are at fault. I assume the problem existed before the black box was replaced.

I have observed on my '01 WR250F (also YZ timed) that the spark struggles to ignite the charge at smallish throttle settings, say 1/8th throttle just accelerating gently. This is noticed as an annoying occasional miss (once per couple of seconds). Also, a sparkplug in less than optimal shape can cause missing/breaking down at WFO. It is almost like the high tension circuit has a very high resistance, meaning that the spark jumps but it is very thin - in fact you can't see it unless the room is darkened.

In frustration, I tried changing the plug gap and noticed much better low speed running behaviour with a larger gap of around 40-50 thou. This pretty much solved the problem for me.

Does yours miss at full throttle or part? Does it miss while turning the throttle or for a while after a throttle setting is established? Is the popping in the exhaust or the inlet tract? Has the carb been "de-octopussed"?

HTH. BTW that's a killer price!


Posted by: SFO---------------------

'02 has no octopuss.
Thanks Strick, now I'll never be able to sell my '01.
2500$?


Posted by: Strick---------------------

Humai:

Thanks for the reply I may be both bugging you an updating you as I go, if you don't mind. The bike misfires in the lower throttle settings, but misses right away, you can't miss it. It does not seem electrical to me. It also backfires (once) when coming off of the throttle (when revving quick while stopped). The consistent miss leads me to timing. I will check that first. Then I will go into the carb. What is the octopuss?

I am currently going through and cleaning and doing routine stuff, like air cleaner, mounting my extra damper, new front tire, etc.

Did I mention it has both stock and e-series exhaust, regina o-ring chain, Tag triple clamp, fatty bars, damper top clamp & post, 3 air filters, all the original parts, manual, iron man sprocket (plus 3 extra), handguards, graphics.... The list goes on and on. That is why for $2500 I had to buy it. I KNOW I will be able to fix it. I am just looking for a shortcut or 2 or 3 or.....

Thanks guys!


Posted by: SFO---------------------

Strick, the octopuss was a tangle of hoses and such on the wr400's.
I might check the float level too.
Here is a sorta similiar thread at TT, I thought of you when I read it.


http://www.thumpertalk.com/forum/sh...b=5&o=7&fpart=1


Posted by: SFO---------------------

Oh, BTW, welcome to blue.


Posted by: Humai---------------------

Quote:
Originally posted by Strick
Humai:

Thanks for the reply I may be both bugging you an updating you as I go, if you don't mind.


No worries Strick, any time!

I still have my venerable 98 YZ400F, which I will probably never sell. This bike as delivered was very lean and hesitant just off idle and would backfire on throttle-off - upping the pilot one size and re-adjusting the fuel screw solved both problems.

Even though your experiments seem to discount the carb, and given that it sounds to you to be not electrical in nature, is it possible that one or more of the pilot, accel pump or needle settings in both carbs were not right? Which of the exhausts are you running? Is the E Series a megaphone type? Perhaps the pipe has changed jetting requirements significantly.

One thing that has helped me diagnose this sort of problem is a technique known as "Exhaust Output Measurement Using Olefactory Molecular Analysis" - sniffing fumes, man, yeah!. Now stop laughing - I'm serious! Sometimes a rich condition causing a miss (wrong Accel Pump setting or worn needle for example) can be detected on a four-stroke by the telltale smell of rich mixture or puff of black smoke. Leanness can produce fumes that can produce eye-watering irritation. There you go!

Good luck with the project and lt us know how it goes!


Posted by: Strick---------------------

Rule #1 never try to out guess an owner of a bike you JUST purchased and had never owned in the past (Humai & JasonJ).

Here is my story and my findings:

For anyone interested. After a lengthy discussion with the previous owner of this WR regarding the mechanic that set up the YZ timing, I felt comfortable in believing it was performed correctly. The gray wire had also been cut, the throttle stop shortened and the BK mod installed. With, what I feel a strong jetting background, I decided to head in that direction.

I first checked the slide plate to make sure it was not installed upside down like some KTM's last year. I then installed a richer needle (OCEMP #5) - simple, quick try. I cold fouled the spark plug within 30 seconds. So, back to the drawing board. I decided just to remove the carb and check out the baseline settings and go from there. Stock needle (DRR #5) 45 pilot, 155 main, BK squirt ~ 2.5 seconds, mixture screw at 2 turns. I then realize I probably went the wrong direction with the needle clip position, and also quickly discerned the jetting was actually somewhat backwards. I change the needle (EMP) clip to #3, I take the mixture to 1 1/2 turns, I install a 38 pilot, 158 main, and time the BK squirt to what looks to be just under one second. Also one other interesting find. The spark plug was gapped like a KTM = .24. I installed a NEW plug at .30. I put in fresh gas, turn on the petcock, pull out the choke, give one full turn with the throttle, go one click past TDC with the kick starter, no luck. Once more - one click past TDC bring the kick starter back to the top, like before, and she purrs like a kitten (except I had the idle turned to high). I give the WR once (or four times) up the street and back, Man does this bike run. No surging, no back firing, just one heck of a pull. The head pipe did glow red when I was letting it idle and checking for any bog or backfire, but I hear that this is a normal occurrence with these bikes.

Thanks for all the responses. I just wanted to let everyone know the findings.



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