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HELP!: Diagnosis needed on a 2002 XR400

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I have a 2002 XR400 and about two months ago went to start it and not a problem....fired right up! However, not to soon after that smoke started appearing from the engine....not pipe! Also, the bike seemed to get a lot hotter than normal and quickly! After trying to figure it out...and I couldn’t, decided to take top end apart. Replaced the rings, lapped the valves, cleaned things up and reassembled (Piston was within specs as was everything else). Fired it up (first kick actually) and wouldn’t you know it....here comes the smoke and heat again. What the heck??? Might my oil pump not be functioning properly (i.e. poor flow not keeping top end cool enough). Clogged oil line....cooler??? I did clean the oil screen near drain in front....looked good! Any and all thoughts appreciated! Thanks!

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Oil filter in backwards? That will block the oil flow and is easy fix. A bit more likely than dead pump/blocked cooler. Good luck with that.

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Nope....all good there! Thanks for suggestion! I'm still stumped...! I might drain the oil and check the lines & cooler the best I can. I gotta start tying something..... additional suggestions welcomed!!! Thanks

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smoke started appearing "from the engine...."

That's a litte vague. Can you be more specific?

Didn't find any gasket leaks around the head or anything that could have been leaking oil and burning off or dripping down onto the header?

Make sure the head vent line is secure at both ends and in good condition. It's that line on the right side of the frame, forward of the gas tank, that runs from the frame reservoir to a nipple on the head.

Does the oil cooler get hot to the touch?

You know, there's a filter screen in the bottom of the engine below the crank too, right?

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Thanks for response....

Yes, all gaskets are good as I replaced them when taking off top end. I have looked and looked and and can't see a leak. So from what I can tell the smoke does not seem to be oil related as it pertains to the outside of the engine. Head vent line looked good too (I'll re-check it tomorrow).

Yes, the oil cooler does get hot to the touch and fairly quickly too! What might this mean?

I do know there is a screen at the bottom and I have not checked it....a good next step in your opinion? Again, when checking the other screen it looked good.

Thanks again for your time....very much appreciated!

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The only other things I can think of that might cause it to spontaneously start running hot is partially plugged jetting and fuel screw, causing a lean condition.

You didn't happen to replace the spark plug before all this did you, Or make any new intake/exhaust mods?

Has it got the proper heat range plug in it?

If the bike is stored outside, I suppose water/condensation could build up in the spark plug well and the first time you start the bike, as it warms up, that water is going to turn to steam and might seem like smoke if you can't tell the difference. But then, you said it did the same thing after putting it back together. Hmmmmm.

Do you still have the stock Calif emissions cannister/crankcase breather separator on the bike? If so, take all that apart, drain it, make sure all the tubing is clear.

Are you sure the oil level in the engine is good/not low? An engine that's running hot, for whatever reason, can thermally overtax an oil, causing it to foam. Foam/bubbles coating your engine internals don't lubricate or conduct heat away from internals and carry to the cooler. It causes engine over-heating in short order and the vapor of it is carried out thru the crankcase vent line. Depending on where that upper vent line is run, you'll smell it and see it.

Your oil might also be contaminated. I'd do a fresh oil change with a good synthetic.

You'll also want to be sure the engine isn't over-filled with oil. I've seen posts that indicate an over filled engine will cause overheating.

Edited by Trailryder42

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