82 YZ490 throttle stuck full open

[mkpack77]

Not sure what happened, I was riding the track, just took a turn, and then all of a sudden, without even touching the throttle, the engine just completely rev'd out. It stays wide open, regardless of what position the throttle is in, I'm fairly sure the slide is working properly because when I twist the throttle I can hear the slide. I had to throw it into a high gear in order to stall it, and if I re-start it, it goes right back to full open. Any ideas on the cause of this, I don't want to tear it apart until I get some tips. thanks

[D tom]

I sent private message.But i'd say yr main jet unscrewed itself or the needle came out of its hole or the circlip came off.Any way you should tear down the carb before riding her again... I wouldnt want my 490 going without my permission on the best day!!!!

[TRexRacing]

My 465 did that occasionally.Crank seals fixed it.Leak it down and check for leaks.

[D tom]

Thats true It probably wouldnt run wide open with jet problems.More like full choke. Sounds more like an air leak.

[Sean9224]

nothing wrong with wide open hahaha

i hope you get it fixed !

[mkpack77]

how would i go about checking it for leaks? how hard of a task is it to change them? don't i have to "bake" the halves in the oven to change them???

[D tom]

your manual has detailed instructions on pressure testing the crank case.

[VAL]

Could have been it ran out of gas. Just before a two stoke runs completely out of gas, it will rev to the moon because of an excessive lean condition. (Running out of gas is about as lean as you can get.) A restricked fuel filter or a stuck float valve can do it as well. I would at least go through the fuel system to see.
Main seals are easy, no baking needed. Look around you intake as well.

How many times did you have to put your chonies through the wash to get that stain out after this happened?

[mkpack77]

yeah i had to wash them quite a few times, luckily it was right before a jump so i had enough time to react.
it's not out of fuel, i'm hoping it's something obvious in the carb but i guess the crank seals won't be that bad. does anyone know of a carb rebuild kit; do they even make em?? the only place i know of to get carb parts is off of the oem yam. site
does anyone know where i can get crank seals from? i know i've seen em on a site somewhere but i can't find it now.
oh and d tom, i didn't get your message????

[nexus446]

Yours does sound like an air leak as if it was a slide sticking then even throwing a higher gear at it would not really stop it, if it is running lean due to an air leak then the power it delivers during the revving out is not that great? if it feels very torquey then suspect carb slide sticking, if not then suspect an air leak after carb or crank seals, pressure test the cylinder to see if the main seals or casing is leaking.
Oh and I had a slide stick on my last outing due to me not running a carb top boot and it filled up with dirt and it stuck about half open just as I wanted to brake and I couldnt stall the engine with full rear brake on! luckily it released just as I bounced over the track side into a field! scary!

[svante]

crank seals is to a yz490 is hard to find IF you dont know that yz250 has the same seals from -76 to -87....which is more common......

check out partnumbers if you like.....
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