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2000 yz125 need help please!

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Hey everyone first off im am new to the site and i must say i really like it

Ok so here is my prob i bought a 2000 yz 125 from somone a couple weeks ago and they said it needed a new top end. I pulled everything apart and he could not have been more right the rings were shot and the O rings that lay on top of the cyl were almost completely melted so there was rad fluid all in the cylinder and crank l. I cleaned all of it up and the cyd looked good, still has cross-hatching. So i ordered a nice top end kit from wiseco put it all together perfectly, ring gap was 13 thousands of an inch, put it in the sleeve, piston moves up and down very smooth, filled it with fluids, new plug and air filter. Today i go to fire it up and im getting nothing.

I have a nice spark compression "sounds great" (can hear a nice sucking noise as it moves) but not geting cumbustion. Now here is where i need help, when i poor about a table spoon of premix down the spark plug hole it starts for about 1 second than dies and i cant get it to start again. Then i will pull the plug, it is soaking wet btw and i can repeat the prosses but still nothing. I messed with air screw and nothing. I also as of right now was trying to run 25:1 for the break in. Could i just have way too much oil to the point where it cant even get a spark going? I am a little stumpped but i will say i have not looked at the carb really at all. Any advise would be great i appoligize for any spelling or gramer i am via iphone thanks!!

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OK...if you have spark, then the plug ain't fouled. You can't test compression by "ear". Put a compression tester on it and see what you get. Should be well over 100psi if you do it right.

The fact that it starts when you put premix in the hole leads me to believe that you might not be getting enough fuel. Maybe enough to wet a plug after lots of kicks, but not enough to start it.

I would pull the carb, clean it thoroughly and check all the jets. If it wasn't ridden for a while, they are probably all gummed up. That would seem to be the next logical thing to check.

Oh....and how do the reeds look?

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Even at 25:1 I would still imagine the bike firing. Your ring gap seems fine, that's what mine was measured at with my wiseco kit so that shouldn't be an issue. Although it took a few more kicks than normal to prime the cylinder, it still eventually fired. How long did you try? Keep kicking that sucker. Maybe your reeds?

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Thanks for the replies guys. Yea the bike probably has not been started in a long time. I have not put a compression tester to it yet b.c i literaly just put the top end back together, it would be a real shame if its not holding enough compressio. Could there be an issue with the jetting b.c i have a feeling the pre owner of the bike messed with it a lil bit. How would i go about checking the reeds sorry if i sound inclinded but this is my first rebuild on a 2smoker im more of an import automobile guy? And zach i was kicking that thing all day and i wasnt getting anything but everytime i put a lil gas down the plug hole i get it going for only a split second.. Thanks for the help very much appreciated

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Just pull the reed block and visually inspect the reeds. Look for cracks (not good!)....or reeds that don't lie flat and thus don't close off the block well.

I really think you need to pull the carb, take it apart, and clean everything, including the jets, really well. I strongly suspect that you just aren't getting enough fuel, probably due to crap in the carb.

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Ok sounds great im sitting at work right now waiting to leave and im going right to the garage and im going to take it apart. Would i be able to tell how big the jets are when im inside the carb for example how do i tell the difference between a 35 to a 45 or a 350 to a 450 is it simply a physical size that i can measure? Sorry again for the poor knowledge thanks

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I agree.. must be the carb. Probably some trash in the jets. Also be sure to check your float level, clean out the bowl. Just spray carb. cleaner everywhere and/or soak it.

I'd also suggest, getting a manual. You can get download one for free by clicking HERE!

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Thanks guys yesterday put in 32:1 drained the carb and she fired up. After that she would only idle with the choke on and would only stay in gear when the choke was up so i cleaned the carb out and it seemed to fix everything. Still have not hit the high band yet still breaking her in but i have a feeling she will rip appreciate the help everyone. Btw when i drained the carb there was like a white substance liquid that came out anyone have any idea what that could be?

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Thanks guys yesterday put in 32:1 drained the carb and she fired up. After that she would only idle with the choke on and would only stay in gear when the choke was up so i cleaned the carb out and it seemed to fix everything. Still have not hit the high band yet still breaking her in but i have a feeling she will rip appreciate the help everyone. Btw when i drained the carb there was like a white substance liquid that came out anyone have any idea what that could be?

Water/oil mixed and set up.

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