1991 lt250r reving on its own
 

Hey guys picked up a 91 lt and its a little rigger but not a bad base but i have a issue... The quad will kick start runs stong when you ride it right. However.... When you start it the motor will idle for a few then all by itself it revs up and down. It almost revs to about 3/4 throttle and goes back down to idle then all over again. Starts off going up to half then will rev higher each cycle. So far i have put new intake gasket with silacone. (it has the boyesen aluminum 22.5 looking elbow with the fernco looking intake boot) silaconed the boot to the elbow and to the carb. sparyed the whole motor top to bottom with soapy water no spitting or sputtering exactly the same. The guy gave me a extra carb put the 2nd carb on after cleaning it did the exact same thing. Then pulled the exhaust valve cover off and checked the valve it moves completly free not spring loaded at all (i check when it wasnt running)... Now for when i road it i took it down the block and barely moved at low rpm then once you got near powerband it picked up slowly then started to scream at about 3/4 of way through the gear. also it revs but almost seems the throttle cable is holding the carb slightly open. However it is not and the cable is new. I tried turning the idle screw and did nothing. The quad has boyesen pro series reed. Boyesen intake fmf fatty and silencer and i was told its on stock bore. thanks in advanced

what does your spark plug look like? Was it jetted for the pipe?

It's either a problem with your slide in the top of the carb (floating or in backwards) or the crank seals are leaking.

I fully agree with that! Exactly what I was thinking while reading the post.

Thanks guys im thinking crank seals but going to look into the carb. I doubt it is the problem unfortunatly .... for jmuddin not sure if the carb is jetted for the pipe I was told one carb is stock and one was jetted but not sure for what. I had both the jetted carb in and now have the stock in. Im going to asume the number will be etched into the jet or will i have to buy a new one? I have a stock rebuild kit with needle stock jets and a couple misc. seals. I'm going to do that but not convinced it will help. Also imo the plug looks good has a slight tint of tan the threads were wet but the electrode looks good... I took it to my buddys this weekend and did the same thing as expected. Although it seems to rev higher. When I let the clutch out its like I have the throttle pinned and just spins. However when I shift it will completly die. So naturally I pulled the clutch in and it started screaming again. Then I dumped the clutch spun 2nd then repeated through every gear spinning.(in snow but good tires). So I sat the day out didnt want to blow it. Any help on confirming the problem? Thanks. Also anyone have a link to a good crank seal thread?

okay so i think i fixed it....... I took the stator cover off to find the one bolt hole is partly broke. Also the stator wire rubber gromet was not in the slot. So I silaconed the cover and put the gromet back in. Then did a full carb rebuild and put a new intake boot on. Then it would not start at all. So I noticed the hose from the petcock to the carb had air bubbles in it so i pulled the ?bolt? out of the bottom of the carb not to much fuel came out. So I took it apart to find the old float valve system was diffrent then the new. So figured that out. put it all back together and the greatest thing happened 2!!!! kicks and it fired and did not rev on its own!!!! took it around the block has great power but at high rpm it falls on its face thinking jetting? It has the stock size jet. It has a boyesen intake setup (cage reeds and the 22.5 looking elbow (not sure if that requires bigger jet) but.... it also has a fmf fatty and fmf silencer... Im told its stock bore but not confirmed what would you suggest for jet im in ny its about 0-35 degrees F now and im about 1500' up. also a question I have is while the motor was reving on its on even when i sprayed it with soapy water and starting fluid all over the intake boots and carb and no change is it possible that the crank seal is bad and it no longer sucks air because it no longer has a souce to suck air from. Or is it some magical intake leak that doesnt change when i spray it... I guess I would like to know if my seal is bad shouldnt I change it anyways rather then putting a band-aid on it by sealing the stator cover.

I think you found it.
Altho, if still in doubt, crank seals a a few bucks and they pry out and in.
Did you happen to look at the seal while you were into the stator?

I think you may need a bigger main jet. If you give it full throttle and it bogs, it's from too much air/not enough gas. Providing I'm understanding that correctly.

I already ordered crank seals after the first replys thanks for the quick responses. I was trying to look at the seals but the flywheel was in the way. Unless that is the wrong place to look the other seal I looked at I would think would be called the counter balance seal. So I guess I should have asked first but I bought a flywheel puller guessing the crank seal is behind the flywheel sound right? .... Do any of you have expierence with the aftermarket carbs? I was looking at the keihn pwk carbs from 38mm up to 40s im not looking to make this really fast (like stroker or big bore) I want it to be reliable!!!! and if I can maintain that with some extra power that would be great any advice on the carb bore I should get.

Yes, Under the flywheel.
I doubt a carb will make much difference. Boring and stroking makes more torque.
Reliable = stock. :)

:yup:

I was thinking the same thing as soon as I read the title-