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89 yz 125 will not start please help!

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I bought a yz125 about a year ago and it sat because the guy said it didn't run right and I didn't really have the time to get into it. well recently I decided to give it a try. I had some premium gas sitting around (no oil in it) and I threw it in just to see if it would start. (stupid I know) but anyways it started first kick and idled perfectly and revved beautifully. I shut it of and then next day I bought some oil and more gas and mixed it 32:1. The bike would not start. I was kicking it over for about an hour sweating my ass off and finally it fired up.YES! It wouldn't stay running unless I was on the throttle quite a bit, I rode it about 200 feet and it shut off. Now it will not start at all. The compression seems okay ( I did the thumb test as I don't have a gauge) I pulled the plug and I have spark. I will say it seems the plug fouls the second it is back in the bike as I have to blow it off before I see spark. Also, the carb leaks gas out of the overflow tube. So is it just my engine flooding? Why would it run beautifully with the straight gas but then have a problem with the correct gas? Oh and just some more info, I'm trying to start it with the petcock off so the carb doesn't overflow. I open it to let the gas fill the carb but then I shut it off. I'm pretty new to 2 stroke. I had a cr250 but I never did any work on it. Sorry if this is like a "dude its clearly your carb" issue but I just don't understand the straight gas running fine and by fine I mean it ran beautifully for the short time I ran it. And also the finally starting and running for 200 feet. any and all help is appreciated.

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Float needle and seat? If the needle has a rubbers tip it may be shot. Sounds like it's flooding. Clean the carb, particularly the needle and seat and check the float height.

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I was just reading through some old posts and remembered that when it ran with straight gas (no oil) the bike did not have the powervalve installed I don't know if this helps figured I mention it. I will clean the carbs this week when I have the free time and see what happens. but any input on the powervalve remove would be awesome.

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Might even be worth while seeing if you can buy a carby rebuild kit any putting that through the carb to freshen the bike up a little. Also did you turn the fuel off between rides? If not, it would've totally floaded the bike. And make shore you let the bike idle/run for a couple of minutes before you start revving and riding the bike otherwise you'll heat seize the barrel and piston and after that its really hard to start. Similar experience happened to my yami wr250 2 stroke so I did those things as mentioned by my mechanic and the bike runs great now as I wasn't too familar with the 2 stroke side of things. Hope that helps.

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Yes I did turn the gas off but I will still kick the bike over without the plug to see if anything clears out. If it got heat siezed would it still kick over? Mine kicks over fine just no fire

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Yeah it'll kick over fine, but will just take a while till it'll start. To me if it ran with no oil haha only fuel it does sound like its been heat seized. If it isn't that the carb will need cleaning and a freshen up especially with some new jets. All the best

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I think what he meant is more commonly known as a 'cold seize' or a 'four corner seize' when improperly starting a cold two-stroke.

 

You have to warm up the engine gradualy to operating temperature before you rev it too high or put a high load on the engine,

reving the piss out or beating on a cold engine will expand the piston faster that the surrounding cylinder with risk of damage or seizure.

 

Even if it doesn't seize, a clue for such issues during disassembly is finding wear/scratches in 4 opposing areas around the piston skirt (aka "four corner seize")

 

 

If you want to help the longevity of your 2 stroke engine / piston, try this procedure for starting and warming it up :

 

-Turn off the choke off immediatly after the engine fires up, even if the engine tends to stall

  Keep it running just above normal idle speed instead by lightly blipping the throttle. (like 1/8 throttle)

 

-During warm-up, don't let it idle at low rpm. From time to time keep blipping the throttle lightly up to 1/8 throttle when cold to about 1/4 throttle

 after the engine has been running for a minute or so. Keep doing this until you can feel the surfaces of the cylinder & head starting to warm up.

 

-Once heat is felt on the engine, go out and ride at a moderate pace (no high rpms / no high engine load) until the engine is fully warmed up.

  During the first 1-2 minutes of riding, if it bogs or stutters don't try to 'clear it out' by revving the engine to the moon.

Edited by mlatour

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Ok I appreciate the reply what can I do about the heat sieze? Just the carb rebuild?

You can't really do much about the heat seize I don't think (or cold seize as mlatour calls it), just gotta keep kicking it over until it'll start that's how I got my wr to go. But I reckon half the problem is the carb aswell. Clean the carb, buy a carby kit for it (that's if you can get one). Once you get it going it'll be an awesome little bike that's for sure!!

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just an update so everyone that helped doesn't think I ignored it,. its too cold for me to do work on the yz for now, thinking of bringing it in the house since I don't have a garage. but I really do appreciate the responses and when I am able I will do the tips and tricks you've suggested.

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