ktm 300exc complete smoke stack

sick 96 250 · Sep 19, 2007

I picked up a 300exc recently that was completely torn down. I replaced, crank bearing/seals, etc within the motor. Got everything assembled and sure enough it fired right up with no issues until I turned around and half my street is a smoke stack. At first I had some issues with one of the o-rings on the head not seating so I pulled that and made sure it was seated properly. Next I figured maybe there is a chance the RH crank seal is shot maybe from being installed wrong but I did the crank breather test with the breather tube in water to see if any air bubbles or anything formed and nothing so I assume thats good. I am at a loss here and this thing is smoking like no other. Low to mid power is real jumpy but higher RPM's is hauls yet still smokes. Piston and rings are new so unless somehow the shop gave me the wrong size and blow by is the only other thing I can think of causing so much smoke. Only other issue I had when putting the bike back together was the exhaust pipe is a real PITA to get seated, could this be enough to cause this much smoke as its not combusting and burning. Below is a little clip of the smokestack.

http://s2.photobucket.com/albums/y44/fox_forma/?action=view&current=smoke.flv

dirt bike dave · Sep 19, 2007

What year is it? Some years were jetted way too rich stock.

sick 96 250 · Sep 19, 2007

its a 2000, the smoke just seems very excessive for a jetting issue which has me thinking the only thing left is the RH crank seal but that was replace along with the crank bearings unless they were installed wrong. What I find odd though is once you get moving a little like 3rd the bike screams. Looks like the right side is coming off again unless I can track it down elsewhere.

alexhack · Sep 19, 2007

Does the smoke smell like premix or gear oil? I would think that would be a possible sign of a leaky seal. What are you mixing your fuel at? Also what do you mean by the low to mid power is real jumpy? Does it bogg or stutter?

sick 96 250 · Sep 19, 2007

premix is 40:1 with Mobile racing 2t and 91 pump gas. I cant really get a grasp on the smell. When I had my rh crank seal go out on my 96 RM250 it was very obvious, smoke was blue/black practically. This isn't white or blue and I really cant tell what the smell is. I think it may be the exhaust flange on the front of the motor isn't sealed up properly. As for the power, its kind of jumpy when in lower RPM's, jetting along with a few other things are getting looked at tomorrow when I wake up so it will be the deciding factor if the side case has to come off for a new seal, which the seal in there is new. There isn't any type of tracer you can add to the gear oil that would make it burn a certain color out the exhaust for proof of RH seal leak? That would be great but I doubt there is.

sick 96 250 · Sep 19, 2007

With the exhaust pipe not sealing correctly to the head would that cause my kind of condition by chance? Just noticed there was an O-ring stuffed onto the flange when there shouldn't be which in turn is causing the pipe to not fully seat itself.

ratso88 · Sep 19, 2007

Looks like a real smoker! If not the crank seal, maybe the spllit in cases. Did you use any sealing compound, gaskets on straight? Is the choke sticking on the carb? A bad seal at the pipe/cylinder wouldn't cause more smoke.

Try posting at ktmtalk. Guys are pretty helpful over there.

sick 96 250 · Sep 19, 2007

already got posts going on at ktmtalk, lol. The whole motor was in pieces and I assembled everything going by the manual and tq specs. I used the gasket for the cases I needed and was very careful to make sure everything went together smooth. Nothing is leaking anywhere so I would think that takes care of the cases being sealed up. Going to try a few things tomorrow, if it doesn't work out then the right side is coming off and a new seal is going in. This time I'm going to do it instead of the shop. Other than this everything operates very smooth, no odd noises or grinding. After I got the motor completely together and in the bike it fired up 2nd kick. I have never had that happen before.

With the pipe not sealing wouldn't that be causing all sorts of exhaust turbulence which in turn can be making half the fuel not ignite properly?

sick 96 250 · Sep 20, 2007

replacing the rh seal tomorrow so we'll see what happens.

jersey devil · Sep 22, 2007

Yes make sure the seal is installed correctly and also check the O ring behind the spacer. BTW, make sure the spacer isn't grooved from the old seal.

Next it could be a pinched inner O ring on the head and your burning coolent. That would also cause a white smoke/steam with little to no odor.

While the exhaust system should be sealed that's not the cause of your current problem.

sick 96 250 · Sep 22, 2007

Got it running today and looks like I'm good to go, at first it smoked like crazy again and I was about to ride the thing off a cliff but turned out to just be the left over oil in the exhaust chamber. Still smokes a tad but I will fine tune it this week hopefully so for now everything seems to be good to go.

Any trick of getting the head pipe to fully seal on this thing? My RM250 has orings which are inside the pipe so when it slips over the exhaust flange it seals. These 300's arent like that so i still get some extra dropping of spooge once its shut down.

sick 96 250 · Sep 22, 2007

Finished Product......
300exc 1

300exc 2

ktm 300exc complete smoke stack

sick 96 250

dirt bike dave

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alexhack

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ktm 300exc complete smoke stack

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