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Freshly rebuilt kx250 smokes like crazy and doesnt sound right... help?

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I just rebuilt my 2003 kx250 from the ground up almost every nut and bolt and all of the engine (top end, bottom end, complete clutch). it has new radiators and exhaust as well. When i bought the exhaust originally it was racing season and i didn't have the time to re-jet the bike immediately and like an idiot i decided to race it while it was running lean and ended up blowing the motor. so i put in the recommended 165 main jet and 52 pilot jet when i re-built the bike. I finally started the bike yesterday and it started with a few kicks and seemed to run ok. But it smokes like crazy. its insane how much smoke it makes, and I don't want to rev it too much to try to clean it out because its a brand new motor. it doesn't have that characteristic castor 927 premix smell either. I've put like 15 minutes of run time on the motor and it just doesn't seem right. It makes a sound similar to the sound you hear when you slowly push down the kickstart once in a while too if you rev it and that kinda scares me.

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is there an easy way to do that?

Leak down test.

You rebuilt the whole motor and didn't do that before starting it??

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Skip the leakdown for now. A cold motor would normally smoke a lot. Try to narrow down where the bad sound is coming from. At a minimum, pull the cylinder and take a good look in there. No need to pull the head and as long as the base gasket doesn't rip, just reuse it.

Running it lean most likely caused some severe damage. But gotta get in there and inspect. With the right tools, cylinder can be off in 5 min.

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Skip the leakdown for now. A cold motor would normally smoke a lot. Try to narrow down where the bad sound is coming from. At a minimum, pull the cylinder and take a good look in there. No need to pull the head and as long as the base gasket doesn't rip, just reuse it.

Running it lean most likely caused some severe damage. But gotta get in there and inspect. With the right tools, cylinder can be off in 5 min.

The motor was just rebuilt. Plated cylender and everything top and bottom end. It almost has to be the right side crank seal. I've had two people tell me that now and that's what I was thinking but dreading at the same time. It must have folded when I put in the crank. now looking into it its loosing oil and starting to dump it out the exhaust.

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Pull the complete clutch/water pump cover from the engine and also remove the crank gear. You can inspect the seal from that side and see if it is damaged or folded inward. You might get lucky and be able to use some sort of plastic feeler gauge material and work the seal back into place if you have not ran it much and damaged it.

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