96 KX500 smoking BAD

[JAYFARMLAW]

My 96 kx500 has always been one of the most dependable dirt bikes I have ever heard of.  I have a v-force, fmf pipe and silencer, and a steahly flywheel weight, otherwise the motor is stock.  

I do not know how old the top end, I have owned the bike for about a year and it is in very good condition.  The bike spend 99% of it's time as a wood/trail machine riding with my son on his KTM SX65.  I dont open it up much at all.

Yesterday, I was jumping some small jumps and climbing  some near verticle cliffs and just having fun,  nothing real fast and 2nd and third gear at the most.  I got on a little straightaway and opened it up and had it pinned in 5th gear.  There may have been a "pop" back fire sound but I  cant really be sure.  It was not loud it if was.  The engine kept pulling and running great like it always had but it was smoking like a freight train.  It still made as much power as always.

I hope that the slow speed stuff just mucked up the pipe and when I opened it up the stuff just started burning off.  It was really a steady stream of smoke, not the usual puff-puff-puff.  These bikes smoke alot to begin with but this was a real noticable change.

The bike has always started on the third kick and a few months ago had 120 psi compression cold.  

What could make it smoke like this?  I really hope to make it thorough another summer before I tear it down, do a top end,  balance the crank, port the cylinder,....

I did not do anything other than ride yesterday.  Everything was fine for about an hour.  I did not add any gas before the problem either.  I run Motul at 40:1 in premium (91 octane) plus a little octane boost.

Thanks in advance for your response.  I will probably tear into this this weekend.

Jay

[greenstreak]

Sounds to me like crank seals.  If your clutch side crank seal goes bad, you suck transmission oil into the cylinder.  That is where the extra smoke comes from.  Check your transmission oil and it will probably be low. 

[ShadeTreeFab]

if it is the seals get the oem replacement ones from kawi, i tried 3 different after market sets
 and they where all junk.

[Purpletj]

Its the clutch side crank seal.

[Friar-Tuck]

 Well I think if the pipe had gotten "loaded up" 
It would have tapered off down to normal levels of exhaust. 
      Unfortunately this may have also been the last the crankseal could take and started letting some tranny fluid get sucked in.
    If you start fouling plugs, the silencer is likely oil soaked also, and riding will consist of just trying to keep the bike running.

A crankcase pressure/vacuum test would verify your seals, along with monitoring the level of your tranny fluid.
  You may even be able to smell the difference of the oil that has gotten on the plug.
As weird as that sounds I could actually smell the gear oil on the plug when my seals went bad.

The bikes have been very reliable (as you also stated) with minimum amounts of maintenance.
  If you ever looked at "The Maintenance Schedule " on what was supposed to be replaced when,
I could never Afford to ride.
      Your final Question was could you make it 'till the end of the riding season. 
 Usually the problem gets worse as the tranny fluid finds it easier to get past the seal, so don't go too far from the truck if she starts running really dodgey.   
  The only way I know of how to strech a few more rides in is to get a hotter plug.  You may run the risk of melting stuff if you transition from chasing you boy on his 65 in the woods to blasting WFO down the fireroad....
   Tuck\o/