91 KDX250 problems

[chris88NY]

ok so i have a kdx 250 and the thing has been riding like a monster forever, recently the bike died out on me, and when i tryed to start the bike up again and the kickstart wasnt catching it was just flying down, also prior to it dying the bike started fouling out spark plugs like every hour or 2 that day. so the gears in the kickstart werent meeting so i replaced all of that and once i replaced and reassembled it the motor just wouldnt turn. but i did get the bike to pop start but once it was started it sounded like it was hungry for gas. i took the carb off and cleaned the whole thing out, cleaned the air filter and i get on the bike and try to start it and i get nothing, so i kept trying untill my foot felt like it was gunna fall off and it sounded like the engine was just about to turn when it sounded like air shot out of the front of my bike and it sounded like a gunshot out of my exhaust. any clues on the damage? since im a mechanically clueless.

 

[julien_d]

fouling plugs that quickly sounds like a bad RH crank seal to me. It sucks in tranny oil right there and can foul out a plug rather quickly. Pull the right side cover, and stator cover, and see if you have any play in the crank bearings by pulling up and down on the crank at both ends.

 

[chris88NY]

would that also be why it feels like air is shooting out when i try and start the bike?

 

[glad2ride]

Air is sucked in through the air filter and sent out the exhaust.

How long has it been since you checked or replaced the top end?

 

[chris88NY]

It didn't seem like just a backfire since there was a pulse of air that shot out of the front that looked like it had oil in it, could that just be the exhaust connection?

 

[rideduro]

fouling plugs that quickly sounds like a bad RH crank seal to me. It sucks in tranny oil right there and can foul out a plug rather quickly. Pull the right side cover, and stator cover, and see if you have any play in the crank bearings by pulling up and down on the crank at both ends.

I think that's my problem also - can the seals be replaced from the outside w/out splitting the cases (using that drill and wire method)?

 

[julien_d]

Negative. Unfortunately the KDX engine design requires that the seals be pressed in from inside the crank case halves. I just finished a bottom end rebuild on my 89, and it really was not all that bad. If you get into this, feel free to post up and I'll offer up the method I used for splitting the cases and removing/replacing bearings and seals and then sealing the case halves back up.

A puff of exhaust coming out around the pipe during a backfire is not unusual. I'd pull the stator cover and see if there's gas/oil mix hanging out in there. Normally the LH bearing and seal sees more abuse than the RH due to the weight of the flywheel, but if it's bad, it's safe to assume the RH side needs replacing as well.

In short, bad crank seals can cause myriad problems. The worst of it is a lean condition, while the bike will seem to be rich due to oil fouled plugs. If you try to jet it to correct the seemingly rich behavior, you can easily trash the motor.

 

[glad2ride]

I will second that the seal replacement requires splitting the cases.

 

[liven07]

would that also be why it feels like air is shooting out when i try and start the bike?

You said 2 times it feels like air is coming out somewhere. You might want to check your head gasket.

 

[chris88NY]

i know i said it two times i can obviously see that, but when the question was answered, if your bothered to read the whole thing, only the spark plug issue was commented on.