i have an 86 LT250r, i just had it resleeved and installed new piston and rings as well. i also installed new reeds,crank bearings and seals. tried 3 different carbs and now back to stock 34mm mikuni. i've tried jet sizes 240 to 190 and can not get this bike on power band. it is a flat dog. it starts easy and seems to have better bottom end than my honda 250r but thats it. any ideas would be great.

 

Could be a billion things.

Some things to think about:

Sometimes rats and mice like to plug up the pipe with nuts and string and everything else they can get their little paws on. Check it out.

They can do the samething with the airbox. Check it out.

Do a compression test. That way you will know where your at with the engine.

Make sure your getting full throttle.

Check out some of these things and see what comes up.

 

thanks for the ideas. i built this bike from the ground up, the pipe is used but the airbox i had to buy new because original air box was melted by the exhaust. i am getting full throttle, i checked that when i put the new throttle cable and mikuni carb on. i think im gonna start borrowing electronics from my lt500 and see if i could be an electrical problem before i start throwing more money out the window. the compression is at 115 psi, but there is only 1 or 2 hrs on the new sleeve and piston. im about ready to call it qiuts on the lt250r.

 

115 psi is way too low on a 250, you should be closer to 200. If you tested it correctly, throttle wide open and kick until the gauge stops moving, then there's your problem.

 

Maybe the rings arent broken in yet?

 

i didnt hold the throttle open. i will try that later this week and let ya know how it turns out.

 

Was it able to get into the powerband before the rebuild? Re-check your clutch adjustment, should be a little play in the cable, a lot of times if they're just a little bit out the bike will seem ok but just doesn't have that hard hit up top. How does the plug look after a wide open run?

Most of the electronics from the zilla should swap over but do the compression test over first so we're not chasing our tails.

 

it did the same thing before i resleeved it, thats what i thought the problem was and because it was bored to the max i had to resleeve. the other thing i should mention is that at high rpm it is breaking up and kind of surging alittle. im gonna take it to my buddies house and ride it in his field so i got plenty of room to open it up and check the plug.

 

That sounds like it could be a lean issue. Pull your fuel hose off the carb and turn the gas on, make sure it pours out steady. If that's ok fire it up and spray carb or brake cleaner around the intake and carburetor and see if it bogs the engine down. WD40 is safer but really makes a mess.

If you don't find anything you might have to build a leak tester and check the whole engine. They are pretty simple, pull the exhaust and plug it with one of those expandable plugs. Pick up a piece of pvc pipe that will fit snug into your intake and drill 2 holes in it, one for a threaded tire valve that has the rubber washers to seal it and another for a low pressure gauge (15psi).

The tire valve should seal up fairly well but you will need to wipe some silicone around the threads on the gauge to seal it up then cap one end of the pipe. Use a hand pump and pump your engine up to about 5psi and it should hold that pressure for 5 minutes, if not start spraying soapy water around to find the leak. Crank seals are always a good bet but you said you already replaced them.

Get a good compression check first though, always start with the easy stuff. Electrical is still always a possibility too, could be a coil or cdi breaking up or even a bad flywheel, they will do funny things even when they look perfect. Check out and clean all your wiring connections, especially the ground. These are fairly simple engines, not a whole lot that can go wrong with them.