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450 exc 2003 smoking badly

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Hi, just got into trail riding and enjoying it, but after second ride out bike started smoking pretty bad! Didn't make any noise or anything? Tried limping it back home but had to be recovered. Oil/Fuel mixed blowing from exhaust joints and tail pipe. The bike has done 160hrs and when i bought it i was assured it had regular oil and filters. I'm well pissed off with bike although it was good when it was going. Anyone had the same thing happen? Smoke did not seem to clear while limping along but eventually stopped (prob coked plug?) New to 4 strokes but any advice/tips on repair, i would be very gratefull. thanks jma46 :naughty::naughty::D

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Did it suddenly just start smoking or was the increased smoking a gradual process? Had the bike been on its side or upside down just before it started smoking? If the crankcase oil breather is still hooked up to the stock location in the carb inlet, oil has an uncanny knack for finding its way into the combustion chamber especially if the oil level is a little high and/or the bike is not otherwise level. When this occurs, the smoking should subside after several minutes of running to clear out the residual oil in the intake tract.

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Beware of used bikes???

This is a tough and a touchy subject. Doesn't sound like you have had this bike for very long.

without a bunch more answers from you it is hard to answer your questions.

Is it possible you overfilled the oil? Did you use premix instead of regular gasoline? Is it possible that the original owner didn't clean the airfilter thus stucking gritty debris in? Is it possible your timing is off.

Like Chas asked, was it gradual or sudden.

I hope the best for you on this as a rebuild on a KTM is gonna hurt. Hopefully that will not be required. You have a fountain of knowledge in this site, use it.

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A buddy of mine just had a very similar experience with his 03 450 EXC.

Turned out to be a broken piston ring. Hope you have better luck.

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BTW, your motor is hosed.

Next time it smokes (if there ever is a next time) shut it off THEN and walk.

It is inconvenient, but 900 dollars cheaper.

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i would go to ktmtalk.com for any question regarding your bike...

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Checked the breather hose which looks dry, do not think it has had oil down it for a long time, the bike was traveling between trails on a tarmac road, the smoke started suddenly? Going to take off valve covers first and have a look in,thanks for yor reply.

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Not overfilled oil, only checked which was ok, only been out twice for roughly 4.5hrs at a time, bike ran fine until smoke suddenly appeared. Bike not tipped over as i was traveling between trails? thanks for your reply

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Thanks for the info, i will try KTM talk. Hopefully its not too serious? i cant afford to put it in to a dealer, not yet anyway, i keep searching for info and try and tackle myself.

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I know this is going to sound redundant. The breather, If clogged can overpressure the crankcase forcing oil from the valve train into the combustion chamber. I saw a YZF one time that pressured up so badly that it pushed the rubber cam seals from the head. Just left big gaping holes where they used to be. The ktm doesn't have any form of pressure release other than the breather. :naughty: Maybe? you can check the piston rings easy enough by doing a compression test or a leak down. I assume since you have the EXC you mostly use the elect start. Otherwise you could compare how hard it is to kick over compaired to before. You still can see if when you kick it over very slowly if you hear alot of pressure coming from the crankcase. that can be an indication of rings or piston. Other than that your on your own. Thats all I can help you with before you actually do a teardown. I wish you luck. :naughty:

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