Uncontrollable High Reving after starting

[shibby7]

I Just rebuilt a 99 YZ250 motor. New gears, bearings, seals, crank, rod, and piston and rings. The bike starts right up, however it instantly wants to rev real high, but will settle back down momentarily and do it again anytime the throttle is moved any. The bike can be ridden as long as you keep moving. When on the throttle everything seems to be normal, but as soon as you let off it runs really rough. Its been a while since I have had a dirt bike but it kind of seems to me that it is heating up too much. One last thing, when the bike is at a stand-still and does rev real high, gas pours out of the overflow tubes.
Thanks for any help.
Erik

[YZ145]

are your float bowls sticking??

[Spitfire]

My guess would be an airleak, possibly a bad base gasket, did you replace it when you rebuilt it?? I think you can check to see if you have an air leak by starting the bike and spray Starting Fluid around the suspected air leak location and see if the idle goes up.....if it does, you definaltey have found your leak. About the gas pouring out of the overflow, I'd try adjusting your float, maybe it's sticking : Good luck!

[Live2ride]

sounds liek an air leak to me but that doesnt explain the gas poruing-did you forget a gasket maybe?

[shibby7]

I put in all new gaskets. I tried using WD-40 to leak test but no noticable change in idle.

[Spitfire]

Well I'm stumped :

[YZ145]

float bowl......float bowl lol, my bike use to rev like that, it turnd out to be the float bowls sticking, give the carb a lil tap.

[crdemon]

Originally posted by YZ145
float bowl......float bowl lol, my bike use to rev like that, it turnd out to be the float bowls sticking, give the carb a lil tap.

iv'e had the same experine with the floats.

[Honda_Rider_XR]

Just open up that carb and fix the little float needle (or replace if necessary) and check that there is proper movement of the float, and it's within spec.

[shibby7]

Thanks for everyones help. I have come to the conclusuion that the bike only revs high after I apply a little throttle. I can not however get the bike to idle either. The bike sounds best when the choke is on. I did take the carb completly apart and did not see anything wrong. I cleaned everything also, but the bike is still acting up. Any more advice would still be appreciated.

[dixienw123]

my guess is there is dirt somewhere in the carb... or ... an air leak on the rubber boot from the carb to the reeds. check that too. how does your plug look after it has been ideling for a few mins? should be brownish. if more whitish to lean mixture(air leak or dirt in the piolt jet.

[crdemon]

Did U check the FLOAT level???? if your floats r out of whack then the bike may be running rich making it bogg. or it may be getting too much gas making it rev out. mabey also chack your needle, also what r u running for jets?

[shibby7]

Stock Jets

[dixienw123]

the less gas the higher it will rev i thought.?

[shibby7]

What should the float level be?

[crdemon]

is it foulen plugs, or r they white?

[shibby7]

It turns out the problem was a leaky crank seal on the left side. I have replaced the seal and the problem is gone. Thanks to every ones input.