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2000 Honda 400 EX Exhaust Smoking

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First off im new here so hello to everybody, second a friend of mine has a 2000 400 ex that i am thinking about getting, and it was smoking really bad so we tore it down and the cylinder looked fine but the exhaust valv:huh:e had about a 1/8 inch of something that looked like carbon buildup but was white on it, could this be from burning oil , do u think it needs valve seats or seals or maybe just a set of rings, it runs fine just smokes and uses about a quart of oil in 8 hrs, thanks guys

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it probibly need a set of rings ... i have a 400ex motor that u use for racing and hill climbing that has done the same thing several times ... the oil ging looses it's tension and compresses into the oil ring grove on the piston ... i bought a heavy duty set of rings and put in mine and it lasted twice as long b 4 it needed rings again..the 400ex runs hot ... even from the factory and the stock jetting is a little on the lean side in most cases.. a little jetting will help with it running as hot ... i have 2 400ex's and 4 extra motors that i keep ready for a swap incase i need 1 ... i ride my machines pretty hard .. if the bore of the machine your are talking about is in good shape i would re ring it and see how it is .. also while u have ot apart you could put valve seals in it fairly easy .. an kill 2 bird with 1 stone .. so to say ... lol... if you have any more quastions about the 400ex just ask .. i have rebuilt many of the 400ex motors and have come across all kinds of things with them .. :yes:

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Ok thanks for the info man, are there any weakpoints or common problems to look for with an ex?

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the only real issue i have had with any of mine is the oil ring... and the rear axle bearings ... but thats pretty much it as far as running and riding ... :laugh:

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I think that is right on, probably leaking oil past the rings, the white ashy deposit is normal and is an indication that the exhaust valve is sealing and holding compression.

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* Adjusted thread title to include issue and model year

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First off im new here so hello to everybody, second a friend of mine has a 2000 400 ex that i am thinking about getting, and it was smoking really bad so we tore it down and the cylinder looked fine but the exhaust valv:huh:e had about a 1/8 inch of something that looked like carbon buildup but was white on it, could this be from burning oil , do u think it needs valve seats or seals or maybe just a set of rings, it runs fine just smokes and uses about a quart of oil in 8 hrs, thanks guys

if i was you i would have head cleaned and have new value seals and bonnetts changed dont go half assed.

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