I just rebuilt the top end of my 87 LT250. IT starts and runs real nice and has lots of power, but it acts like it is leaning out as if sucking air somewhere. I can't figure out why. I have checked with carb cleaner while the bike was running for air leaks all around the reed cage, carb boot, etc and seem to find nothing. I didn't change jetting in the carb at all.
It can be idling fine one minute, and the next the engine just races like it's at full throttle. If I ride it and hit the gas, when I let off it stays at high throttle, I have to feather the clutch to bring the revs on the motor back down. The throttle cable works fine, nice and smooth and it doesn't change when I turn the handlebars, so it is not bound up at all.
The only other thing I did was wash the foam air cleaner out. Now that I think about it, I didn't reoil it...could that cause the problem? It's not a K&N...more like a UNI FILTER.
Any thoughts on any of this?

 

Yea oil the filter and it should run fine.

 

It will run really lean with no oil in the air filter due to not having any restriction to the air flow. OIL IT ASAP!!!!!!!! because it is also not restricting the dirt flow!!!!!!! Did the problem start after you cleaned the air filter? Also check the slide in the carb to see if it is wore and is getting bound up in the bore of the carb. USE FOAM FILTER OIL NOT MOTOR OIL I have seen to many people using the wrong oil. After a few days all the motor oil will be in the bottom of the air box.

 

The filter not being oiled would let more air in as the others said creating a lean condition, however I'd find it odd that it's varying problem. I would be sure to check that your base gasket is not leaking. It's a common thing to leak on the LT if the case and cyl. base surfaces aren't perfect. The best way to check is with a leak down tester and soapy water. If you don't have one, you can run the engine and spray starting fluid, or use propane around the base (and head/cylinder mating area while you're at it) and see if the idle responds

 

I have K&N oil here from my car's air filter. I'll use it. I can't say the problem started when I cleaned it, because I also rebuilt the top end of the bike at the same time. I am hoping this is the only problem. I checked all around the cylinder base and the head with carb cleaner, as well as the reed cage and intake boot. The idle didn't change noticeably. I will try again with starting fluid just to be sure. Hopefully the oil issue cures it

 

NO NO you can't use k&n oil for a foam filter.

 

Well, thanks for that bulletin of info, but could you elaborate?

Doesn't matter much anyway. I oiled the filter and ran it for about 20 minutes today and the thing quit and has no compression. So, the top end gets to come apart again this week, only two days after it went back together

 

I don't why but i do know theres a harmful difference in the oils. Such as the k&n might break down your filter. The two companies ( uni and k&n) just say to use k&n for paper filters and uni for foam. Man that sucks about the no compression.

 

I would agree with QR, especially after two top ends, check the crank seals real well, if your going to do the top end again I would do the seals anyhow!! I think the kit is only 25-30$ and not that big of a deal to change, and well worth the extra time!!

 

Welcome to the LT250r club!!! The problem can only be a few things. Try taking off the fuel petecock, that could be causing fuel restriction if it is clogged. Cheak all of the gasket surfaces. I had a problem similar with my 87, after a complete rebuild and a carb replacement to a 37mm airstryker it ran like beast! Most good atv shops have an air-fuel machine to cheack jetting, it is well worth it!! Good luck!