Bike revved sky high at startup and won't start anymore

Got a 04 125sx, recently did top end and rode it at the track once or twice, I had washed the bike since I went to the track last, Bike sat for about a week and a half, I cleaned and oil'ed air filter this morning and when I went to start it, Normally my idle screw I have it basically all the way out, and It will still idle alittle higher than I think it should. I put the idle screw in based off another yamaha 2 stroke bike like a normal position for it, When I started the bike it revved all the way out and I killed it as fast as possible. Than I loosened the idle screw all the way out again because that's the way it normally is. Wouldn't start anymore, Changed spark plug and didn't change. The bike just won't start anymore. Any ideas on what happened? Or why my idle screw has to be all the way out and still have a high idle? I don't understand it at all.. I just need answers! Lol

Clean the carb, go back to stock jetting specs for your bike / temp / altitude and retry.

Figures it would be something with carb, I hate carburetor's so much, Everything i've owned with a carb if I let it sit over a week without starting it doesn't ever run again. Lol

If you don't already, when you're finished riding, shut the fuel petcock off and let it idle until the bowl runs out of fuel. This will help keep your carb from gumming up when the bike sits for a period of time.

lol I have 8 carbed motors  3 have 3 carbs each   no issues with sitting a few weeks

  but on a 2 stroke a runaway can scare the crap out of you   so being in gear and being able to dump the clutch is nice  vs  a pwc  with no way to kill it other than dumping fuel or blocking the inlet

I've always just had terrible luck with carb'd stuff. I'll have to remember that tip Supr Sloguy. Last time I rode I was going over a big tabletop and ran out of gas right as I hit the jump. Talk about a big nose dive that was pretty scary. Luckily nothing happened besides a hard front landing. Going to give it another shot at starting it later. Possibly was flooded? If I can't get it going i'll pull the carb off of her and see what I can do with it.

My old yz's always did that when I would first start them. I speculated I didn't give enough time for the bowl to fill with gas, because every time after I killed it, it would start up again, idle, and run with no issues.


Learn some jetting, too. It probably wouldn't start because you just closed the intake completely when you took out the idle screw.

It's possibly you smoked the top end when it screamed at start up. Does the kicker still feel the same afterwards or a little easier to push over? 125's all feel blown up to me, but can you tell a difference.

Make sure you don't have the pilot circuit crazy lean causing the high idle, close your air screw a half turn and try starting it. Can you normally start the bike without the choke or do you always need it?

From the sounds of it, I'm going to take the carb off and go through it. I've never even seen the inside of a carb. All i've done was take off the bottom spray carb cleaner in and it usually fixes most my problems but I guess i'll finally go through it because it seems to keep giving me trouble. Anyone know any links to some good information or guides on cleaning the carb and rejetting? I was looking at jet kits online and there's one called JD Jet kit that seems like it's very simple comes with all the instructions on how to set it up and all that.

My old yz's always did that when I would first start them. I speculated I didn't give enough time for the bowl to fill with gas, because every time after I killed it, it would start up again, idle, and run with no issues.



Exactly  we crank with the PWC  lanyards out to get the carbs  to fill  first   then they will start fine

If it was my bike and it did that.... Id think "no fuel". It reved on the fumes then there wasnt anything left.

Second thought would be throttle cable pulled off at the bars or top of carb.

Check those things out to start.

All problems solved! removed throttle cable, Took off the carb, took out the float etc, let everything drain out, cleaned it out with carb cleaner, Put it back together and installed carb and throttle cable. Started up first kick without choke but wouldn't idle. Which I was happy because Than I tried screwing in the idle screw like a normal bikes position and it still idled alittle low. Another half turn and it runs like a normal bike! Took it down the road to test it out and has alot more power than before. This thing is actually turning into a bike now! Ready to take it to the track again. I've already put new top end on it, New wheel bearings, new front tire, new filter, Gear oil, engine ice, all mainetence stuff. Next on the list is a new rear tire and tube. Excited to take it out again!

good deal

and if it was a  lean runaway  remember it can't do that when your in gear and riding it  so  it won't  ever be like a bad Keanu  Reeves movie

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