02 yz 125 stall at full throttle

dkb

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#1
Hello everyone, I need a little help. I have a stock 02 yz 125 with a 410 main, 30 pilot, needle in the third, grove air screw 2.5 out. Clean air filter, emptied and cleaned gas tank. Fresh gas. 40:1 (yamalube) and new plug. The thing fires up first or second kick. Idles smooth. It runs great up to 3/4 to 7/8 throttle. But at full throttle it dies. DEAD. It won't re-start when I slow down or down shift. If I hold the clutch in till the engine stops turning and then pop the clutch it fires back up. or come to a stop it will kick start the first time. I didn't change or mess with the float level. I checked all vent hoses and fuel petcock. And cleaned the carb. at least 7 times. Same thing death at full throttle. I also checked the few electrical connections I dared fool with. Is this a cdi problem or ignition problem? I'm about to take it to the dealer :eek: Thanks for any advice Darin
 
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#2
My bike(02yz125) did the exact same thing when I first got it. We cleaned the carb out and had a local mechanic check it out before we finally took it back to the dealer which is more than a 2 hour drive. It never would do it for the dealer. It went away after about 10 rides, we never figured it out and it hasnt happened since. I thought it was just my bike. Sorry I wasnt any help but your not alone.
 

atc3434`

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#3
Hmm... I know you've checked the float level, but its still sounding that way to me. You sound like you know your stuff already, and have covered the basics, so I won't hit you with my usual jetting link to Eric Gorr's site. It sounds like it runs the float down when you get it wide open, and the motors gotta stop before it can fill up to start again. I don't know that I buy into that though, even though I just said it. Another thought I have is that its mechanical. For some reason, that motor has to stop to come back alive. That strikes me as very, very odd. If it was cutting out, but would come back on, I'd believe carb or ignition, but it staying off is very, very weird.

Does it do it in neutral if you pin it a second or two?

Does it do it the minute you go wide open, or after it reaches a certain RPM?

This is a very interesting problem, hopefully a few more guys will brains will jump in and we can help ya figure it out.
 

dkb

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#4
Thanks for the replies. It will rev when pinned in neutral. A slight miss at wfo. It also has popped and back fired a few times when I tried to clean it out or re- start after the mystery sign off at full throttle. I didn’t (don’t) have any way to check the float level. The little tab is pretty stout to get bent by accident . I don’t know what’s up
 

atc3434`

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#5
Hmm... its definatly an odd odd problem. I'm thinking its carberation, if its acting normal without a load. Which would lead me back to float height and main jet questions. I know you've been over both of those, maybe just check them again. I wouldn't think the problem would only appear under load if it was electric, but stranger things have happend.

Somebody with some real brains will probably jump in here soon and give you some more to go on, thats all my little brain can kick out. Its tired after doing wheel bearings, a new tire, the filter, and tranny oil. Long day of maintence!

As an after thought while spell checking, how do the reeds look?

Another after thought, back to one of my questions, does it do it immediatly at WOT, or after it hits a certain RPM? This might be a clue...
 
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dkb

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#6
. Thanks for the thoughts act3434' the bike dies at wot not at a given rpm. I thought the reeds would mostly effect the bottom end. The bike has few hours on it (embarrassing to say) and a few times I was able to ride at reduced throttle and it did straighten up and run at wot. But after cooling down it would act up again.
 
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#7
I would try raising the float height just a little bit to eliminate it as a variable. Its not really hard to do, either. My bud landed hard on his bike and we had to readjust the floats since it was doing exactly as you said it was doing, only not above 1/2 throttle.
 

dkb

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#8
derekk87 and anyone else interested. I went back to the garage to try to figure out he problem again. I took the bike out and it stalled a few times in higher gear full throttle roll on. Then I ran it in the lower gears and it revved to the top end just fine. Long story short it started to run like new again. I didn’t ask any questions I just put on the rest of my gear and rode the dang thing! It takes me 10 min to put my gear on (I’m old) and it started and ran fine for 20 min. (I'm still old) It got dark and I got tired but I am happy tonight. Tomorrow I will try it again tomorrow :yeehaw:
 
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