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mxyves

can't solve the problem!!

31 posts in this topic

Help me out here...

my wr426f doesn't run smooth. on 1/4 throttle the engine starts to stutter. If i stay in this revelationrange it keeps stuttering. When in open the throttle wider, it stops to stutter and runs well. We've tried everything to solve the problem: new sparkplugs, cleaning the carb, needle adjust, jetting adjust, cleaning all electrial conections. Nothing seems to help.

Does this sound fammiliar to anybody?

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Hello mxyves,

Have you tried an other CDI? Or could it be the bobine-coil?

Succes,

Foxkid

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My 02 426 was doing the same thing and I kept thinking it was jetting. Then JD said to try unplugging the TPS. I did and it smoothed right out for constant running but I still think it runs better when it's connected when I'm riding trails.

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My 02 426 was doing the same thing and I kept thinking it was jetting. Then JD said to try unplugging the TPS. I did and it smoothed right out for constant running but I still think it runs better when it's connected when I'm riding trails.

Yeah my suggestion would be to try unplugging the TPS and see if it helps, then go from there. The inherent mid range sputtering issues with the TPS are not that bad and only become a nuisance while cruising down a road or something at a constant low to mid RPM.

Good Luck :applause:

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What is a TPS? Is that famous grey wire?

TPS = Throttle position sensor. Look on the left side of the carb and you will see an electrical unit held on by two screws. Follow the wires coming form it for a couple of inches and you will find a connector.

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That is a jetting problem pure and simple.

You are rich on the needle. Drop it one clip and check. If too lean then,

try adding a tiny washer to shim the needle up 1/2 a clip.

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That is a jetting problem pure and simple.

You are rich on the needle. Drop it one clip and check. If too lean then,

try adding a tiny washer to shim the needle up 1/2 a clip.

I agree. Sounds rich.

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I agree. Sounds rich.

It might be but it can't hurt to try disconnecting the TPS and see if it helps. I jetted mine three times and the constant throttle miss wouldn't go away so i was getting :applause: Disconnected the TPS and I loved my bike again :bonk:

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Thanks for the updates!

I'll disconnect the TPS-sensor first (easy job) and see what the bike does. I played too much already with the carb and it doesn't help one bit sofar.

But what if it helps; losing the TPS-signals. No problem to keep it disconnected?

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forget my last question. Great tool this "search" button....

I'll try it out when it's day again here.

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I played too much already with the carb and it doesn't help one bit sofar.
Does changing the needle position make any difference at all? If it stays EXACTLY the same, I would be checking for air leaks. Measure your float height too.

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That is a jetting problem pure and simple.

You are rich on the needle. Drop it one clip and check. If too lean then,

try adding a tiny washer to shim the needle up 1/2 a clip.

I had what sounds like the exact same problem. I fixed it by doing exactly what Matty05 said to do - dropped the needle one notch to lean it. Cleared it right up.

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I would try a leaner pilot jet and see if that clears up your stutter, you may have to go two sizes leaner to clear up your problem.

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Does changing the needle position make any difference at all? If it stays EXACTLY the same, I would be checking for air leaks. Measure your float height too.

Air leaks? Where could I find an air leak on the bike?

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Air leaks? Where could I find an air leak on the bike?

The boots around the carby come to mind, exhaust leaks tend to give some good cracking.

Start your bike up and suss out around the carby. Inspect rubber boots for cracks, airbox boot too. A gentle spray around with soapy water is a good way to find leaks.

Is the stuttering a popping/crackling sound or does the bike feel like it is running real rough/stumbling/cutting out?

I still say drop the needle one or two clips.

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I "lost" the TPS signal but it didn't solve my stuttering-problem unfortunately.

qoute "Is the stuttering a popping/crackling sound or does the bike feel like it is running real rough/stumbling/cutting out?"

When I pull the throttle 1/4th, it smoothly comes up to the max rev's for a quarter pulled throttle. When I slowly turn it then to 1/2 full throttle it starts to fall away like I would be pressing the "turn-off" button several times within a few seconds.

The clip on the needle is now on position 3, which is half way up I think. Should I lower the needle and place the clip on the highest clip-position as possible to feel the effect?

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You are definately rich on the needle, just lower the needle 1 clip position!

You might need to get the next leaner needle from Yamaha. Either that or

A JD jetting kit. Are you going the right way when you change the clip position?

Hold the needle how it sits in the carb (pointy end down, clip up top), top clip is the leanest clip position, #1.

Don't worry about air leaks, it doesn't sound like you have any.

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Thanks for your update. I'm reprosition the needle.

About the leaner needle; leaner like in less thick? What does it do more or less and what effect does it have anyway?(sorry I don't understand)

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