Overheating 87 LT250R

[ChewyR]

I've been chasing this problem for a while. Basically under extended WOT my LT blows heavy steam out the overflow. Is it possible that a bad waterpump seal could be causing this problem as I know it is common on these machines for it to go bad.

I have replaced the radiator cap, changed the head gasket, retorqued numerous times, and done what I've could to lap the cylinder head flat. Also I run redline water wetter to keep the coolant tempreture down.

The bike still runs hard and maintains its compression around 180 psi.

[sblt500r]

a bad water pump seal won't cause that. it will cause coolant to leak out the weep hole or leak into the crank oil. you might want to check the impellar, and flush the system. and while yuor checking the impellar make sure the waterpump shaft isn't broke, it happens.

[diesel-mech]

Did you get ths problem solved? I had the same problem on my tecate4. The jetting was making it over heat. 1st off figure out what part of the throttle range makes it over heat. If it is ok unless you really ride it hard than your main jet is to lean, if it only does it cruising around at 1/2 throttle than its the needle thats to lean, and just putting around its the pilot. You may have to hook a tow rope to another quad and pull it around put enough load on the engine to see just where you are lean but I'm sure you are somewhere. Like I said I just went through this problem on mine. You are losing horsepower too because of it being too lean, I gained 4 horsepower just by getting the jetting right. (we did mine on a dyno)

[saynoto4strokes]

I agree with diesel-mech, you could have a lean issue. Check your plug and see what it tells you. Have you done any recent mods or made any changes? What do you have performance wise (pipe, reeds etc.) and what jet size are you running? Theres not much to these cooling systems either though so if there is a problem it shouldn't be hard at all. Keep us posted. saynoto4strokes.

[370banshee]

also check your radiator cap... it might be bad and not letting the system pressurize.... if the system doesn't pressurize it overheats quite quickly... for every 1 PSI of pressure waters boilign point is soemthing like 8 deg higher

[arcsum68]

Originally Posted by 370banshee

also check your radiator cap... it might be bad and not letting the system pressurize.... if the system doesn't pressurize it overheats quite quickly... for every 1 PSI of pressure waters boilign point is soemthing like 8 deg higher

He did mention that he replaced that, but I suppose he could have gotten a new bad one.

[ChewyR]

I haven't had a chance to mess with it, I broke an ankle putting my street bike down. But when I'm up and moving again in a few weeks I'll jet it up on the main a couple sizes and see if that helps. Hopefully that is all it is, but I'm thinking a cracked cylinder around the exhaust port, because really the problem has been getting progressively worse.

It's only under extened full throttle when this happens. Funny thing is I have been thinking it was slightly lean for a while now, but when I would do a plug chop I would get a slight smoke ring so I thought it was okay. Also it was holding compression ~180 psi after a year of riding so I must not be lean enough to be burning the rings up.

Currently it has a 280 main right now, but I know that it seems to run clean up to a 310 or so. It's a 35mm TMX carb, FMF pipe/silencer .060 Wiseco, Boyesen reeds, and I rechambered the head a little. Runs with 50:1 Amsoil Interceptor on 93 pump gas.

[saynoto4strokes]

Just for the heck of it throw a 310 in there and see what happens. The worst you'll do is foul a plug. And you said a smoke ring? Are you talking about the smoke out the exhaust? saynoto4strokes.

[370banshee]

i didn't read his whole post... thats why i missd the rad cap thing...

[blaster911]

well if its over heating did you try to check the fins on the raidaider to see if they were dirty?