Hi, I Have a 125cc coolster ATV-CL and i need some help. Its running fine,but its has open throttle on start up. It idles well, I purchased a new carb too. Also it wont start with the choke OFF i have to raise it a bit. I've checked the throttle line to check if it was seized or kinked but its fine. Any ideas? Thanks

 

Disconnect the cable entirely to put that out of the loop. Make sure the carb cylinder is actually on the notch (where the throttle screw screws in). Clockwise will make it idle higher.

Verify you have all the carb spacers (intake) on correctly, some have o-rings to seal and I've seen them put backwards or upside down to create a vacuum leak.

 

Hey, I recently rebuilt the head yesterday, went to start it this morning and on start up its has this high rev problem again. Also, the motor makes this loud combustion noise,(on start up) which happens and i immediately hit the the kill switch. The engine also wont stay on for more than 2 seconds then will die. The clip was raised second to the top
so i lowered it back to center point. (5 position needle) I've also been adjusting the idle screw. Any ideas guys thanks!

 

sounds like a sticky slide, or maybe even reversed. leave the air filter off and look down the throat of the carb when you start, the slide should be all the way down. Vacuum leaks shouldn't make it rev, it would run very rough since it would be really leaned out. if the slide is all the way down, it's possible you damaged some of the adjustment seats. If you turned the af adjustment screw in and cranked on it. maybe the needle isn't seating properly at idle?

 

Sorry, but I 1000% disagree. My sons quad had the exact thing I stated on backwards (carb spacer) by the previous owner and the throttle wouldn't come down. He ended up flying off the quad because it kept accelerating even when he let go of the throttle.

 

The thing is you just mentioned 2 separate problems. 1) carb spacer vacuum leak and 2) Throttle slide wouldn't come down. The carb spacer has nothing to do with the slide going all the way down. What was happening in your case would be something above idle coupled (stuck throttle causing it to race the engine) coupled with a vacuum leak after the carb which let in extra air that wasn't metered through the carb. Having a spacer on wrong cannot effect the carb slide. Even in the case of a vacuum slide, the vacuum to raise the slide is from air coming through the carb, not after on the intake. At idle, without a stuck throttle, a vacuum leak will make an engine run very rough. At speed it will lean it out, though the effects lower as the engine speed and regular throttle opening increase because it is a fixed amount of extra air entering the intake. EX. at idle, you have a very slight opening of the carb slide and say you leave a vacuum tube off. In that case, that extra air with throw off the af ratio by 50% and the engine won't start. WOT, like the case of your stuck throttle, you have for example a 30mm carb opened all the way up and a 1mm air leak. It will run like that, just slightly leaner. With that engine, it would stumble and die when the engine returns back to idle. So, just one more time, vacuum leaks (and only vacuum leaks) will not make an engine rev.

 

Want further proof, you can do an experiment yourself. Drill a hole in your intake after the carb or use a vacuum hose hole if it has one. Start the engine with your finger on the hole, then take it off. I will bet you a million dollars that the engine either dies or runs very rough. I will give you my house if it perfectly revs up to redline (without touching the throttle).

 

I guess what is really about to get me riled up is that your giving me this long *** scientific explanation on how a carb works. I gave a "real world" example of what happened that came close to killing my son. Then you tell me to drill an effin hole in my intake to prove what happened didn't happen. I ended up finding the issue and flipped the spacer around and then it had an o-ring sealing the "vacuum leak" that doesn't cause wot like you say. You are a fricken moron.

 

Do not listen to that idiot. What he doesn't seem to realize is that if his intake seal was causing his carb slide to stick open, it was a physical obstruction and not the vacuum causing it to somehow stay open. Sooo, check for physical obstructions, a vacuum leak by itself will not cause your engine to go wot. Despite what that asshat said.

 

Stop it the pair of you. The fact is, a weak mixture does tend to raise the revs. You can easily check this by leaving an engine on idle and turning the fuel tap off. Just before it runs out of fuel, the revs rise. If an air leak happens to be just the right amount to do this, the engine will rev up. Too much and it either dies or runs badly.