Engine revs up to wot by itself?

[85 250sx]

ok i tried posting this in the Jetting thread but didnt have an luck on feed back so hoping this helps. I recently picked up a little project, and well it has what looks to be a new carb on it. It fires right up, but as soon as it does it just starts to rev uncontrolably. what do you guys think this could be? since the carb looks to be new im guessing its never been jetted corectly and im not even sure its anywhere near were it needs to be. ive checked the slide and it does not seem to be stuck at wot. Thanks for any help!

[yaegerb]

is the cable operating correctly..i.e., thumb throttle working appropriately, cable not pinched in the frame somewhere?

Also, when you operate the throttle without the engine running can you hear the slide drop all the way down against the seat of the carb throat?

[Vealmonkey]

Whatever you do, don't tell anyone what the fricking project is, or if the engine is 2 stroke or 4 stroke or anything like that!!!!!! You'll get so much help by people taking stupid guesses. We are all fricking mind readers you know.? Some people never cease to amaze me.

[85 250sx]

sorry there vealmonkey didnt mean to piss you off. its a 200cc four stroke. Yaegerb yes i have checked to make sure the slide goes down the whole way and when the bike is off you can hear the slide hitting the seat of the carb.

[sp8twn]

Iis the carburator intake boot cracked???

[shortline10]

slide needle clip missing ?

[Vealmonkey]

The thing is, symptoms from a 2 stroke and 4 stroke are different. Plus the machine can determine the possible causes, that's all. Firstly, do you have a shop manual? They are something you can't live without. If you don't have one, get one. Secondly, you have to go from simple to hard. Cable routing, cable pinching, dirty air filter, Properly set up or properly functioning carb. Just because you can let off the throttle cable and hear the carb slide seat, doesn't mean it's seating against the bottom of the carb. The idle screw is what holds the slide open and increases the rpms at idle, so, if you don't have your idle screw all the way loose, then what you are seating against is the idle screw and no idea where that is set at. Does the carb have the proper slide? I've seen it done where a previous owner just put in a slide that wasn't for that carb. That was a head scratcher for an hour or 2. Or a previous owner had removed material from the slide for better performance, seen it. A bent needle in the carbs main jet or even no needle at all or a modded needle that didn't go down in the jet hardly any. You really need to get out and start doing some serious trouble shooting on this machine and give us some more detailed description of what it is you have going on right now please. Now get out there and get us some info! NOW!!! LOL

[Slingblade]

An air leak is probably your culprit. Intake boot like mentioned by sp8twn is a good place to start.

[Dirtcrasher]

It does sound like an air leak. Or possibly the carb is not filling up fast enough before it runs dry and a carb running out of fuel is like a very lean carb mixture.

Numerous things could cause this so get you thinking cap on and have at it. G L !!!!!!

[yaegerb]

I am going with the consensus here, which is you likely have an air leak. Spray bottle and soap or another cool trick that I learned from KbOnly is turning on a butane torch just enough so you can smell the gas coming out and then start your motor and wave the nozzle around all your gaskets, intake, etc and when the idle goes higher then you know you have an air leak.

Good luck to you and keep us posted of what you find.

[oscarmayer]

it coudl be he has the slide in wrong. there is a small sized alingment pin on 1 side that the groove on the slide goes through. is you are not alinged up right it can "sound" liek it's bottoming out, but it's now. take the top off and look to ensure your slide is in properly. i have seen this exact smae issue and the slide was not in correctly.

try that before anything else. you should have to stick your finger in there really far to feel the slide. the pin is usually on the opposite of the carb as the idle screw.

[tri again]

it coudl be he has the slide in wrong. there is a small sized alingment pin on 1 side that the groove on the slide goes through. is you are not alinged up right it can "sound" liek it's bottoming out, but it's now. take the top off and look to ensure your slide is in properly. i have seen this exact smae issue and the slide was not in correctly.

try that before anything else. you should have to stick your finger in there really far to feel the slide. the pin is usually on the opposite of the carb as the idle screw.

I've seen that many times and have even done it myself a few times.

Hey, what's the death rev on a 2 stroke?
is it like a gas engine model airplane speeding up right before it runs out of gas?

[85 250sx]

sorry guys havent been home in a while. but i did get time to tear it apart today and did find that the slide was not in the correct position, its a round slide and i guess who ever owed it before me just slid it into the carb and didnt check the markings on the sides just kinda threw it in. after i put it in the correct position it actualy does sit well and now does idle fine. thanks everyone!

[kb0nly]

Awesome! Nice easy fix.