2 Stroke Dirtbike Engine Issue

[Nazo]

I picked up a 1995 Honda CR250 and its all original bone stock.
I rode the bike like 3 or 4 times and it ran perfectly fine, But now it runs not so well.
The RPM's seem to sore and it just high revs like crazy. Even if you just blip the throttle the RPM's scream and don't come back down for a few seconds. It sounds really lean too.
Its not smooth at all, the engine literally jumps and compresses the suspension. It doesn't sound healthy.
The bike does start right up no problem still.

-Appears that air is seeping in possibly as suggested by someone?

What I've done is taken out and gone through the air filter, carbeurator, intake and reeds. Everything appears fine.
I took the carb apart as well. The slide works fine and bowl is not stuck.
-I remember reading somewhere that this was a symptom of needing a new top end......But I forget why (that doesn't make sense to me)
I also know that on some 2 strokes the exhaust flap/valve were prone to getting stuck....But I'm not sure these symptoms would make sense for that being the problem.

-Any thoughts anyone?

[stoinkythepig]

The thought that it's running lean and revving up make me think air is getting into the crank case through a leaky seal or something.

Pure speculation on my part, never dealt with one of those before.

[capt1014]

IT's a very good speculation! check the seals.

[stoinkythepig]

Originally posted by capt1014
IT's a very good speculation! check the seals.

Well there, that's two votes on the internet so that must be it.

[Nazo]

Wow, I think you might be right. I had some coolant leaking out down by the crankcase. I haven't been able to locate the exact point of the leak....But there must be a bad seal somewhere.

I wasn't sure if air in the crank case would do that.
I've had the bike running with the oil filler cap off and it ran fine in the past.....regardless.

Thanks, I think that might help me.

[stoinkythepig]

oil filler cap? this is a two stroke right? Thinking the oil would only be for the transmission, not the crankcase if it's a two stroke. So having the cap off should make no difference i n the way the engine runs if I'm right. Again, pure speculation. I have zero experience with these, but I did stay at a Holiday Inn Express (several of them, they kinda suck but in a very reliable way).

[Nazo]

Yeah your right, tranny is sealed off from the engine.....Brain dead moment there. Been working too hard in the office today I guess.
Thanks for the help, I think your right on the money with my problem.
Awesome, looks like I can make it back out this weekend!!!

[SQUIZZ636]

stupid ? but you did check your cables right because if they are sticking it would do the same thing. but i would think that you already did that.

[SQUIZZ636]

is the coolant leaking out of the front of the cases? it could be coming from the base gasket. the cycl. nuts can back off some times causing the colant to leak out the front and then boom.

[ChR1s]

Try a leak-down test? Might've blown a crank seal. Any unusual smells or smoke, like crankcase oil getting sucked in & burned?

Also, a clogged main jet can exhibit lean conditions, but usually it bogs when given substantial throttle.

[Paul_E_D]

Good leads here. I would check the basics before tearing into it for case sealing issues. Reeds, air leaks around reed cage or exhaust flange. Head/cylinder bolts and o-rings. This would give you a chance to look at the piston as well to see if that's in one piece.

[SSearchVT]

It sounds like it might be a leaking base gasket or cracked reeds. What does the plug look like? Check the torque on the base and head nuts first. An easy ways to check - with the engine idleing srpay some carb clean on the intake boot, and around the base gaskets and listen for any change. The reeds are easy enough to check, pull the carb, and it should be a few bolts holding the boot on. If it is the base gasket, you might as well throw a new top end in it while it's apart. Good Luck...

[R7]

I had a 2-smoke quad (banshee) that ran just as you described... I replaced the reeds and it ran great for another 2 years BTW the reeds looked perfect when I checked them

[Nazo]

The reeds appear to be fine, but I think I'm gonna replace them and do a new top end as well just because its all original from 1995 and its pretty cheap and easy to do.

Thanks everyone for the advice. I think it may be an issue with either a seal or backed off bolt as suggested above.

[Tabby]

The tranny on a two stroke isn't totally seperate from the crankcase. The seal on the primary drive side of the crank, is exposed to tranny lube. It should be looked at too.

[Cue Ball]

Sounds like a head gasket to me, my kx500 did the same thing.