I tore down today and WOW!! There is almost an 1/8" carbon build up between the piston and valves (half on the piston, half on the head).

I run the s*** out of it and use good 93 octane gas. Any knowledge on what is causing this and how to stop it??

I would like to know before I reassemble so I can stop this from happening. Thanks for the help!

 

Well, you're either running too rich, or you're burning oil...

I run Mobil1 15w50 to eliminate a smoking problem mine had since break-in. When stock, I had a modded airbox, and was 165 main jet & 42 Pilot @ about 1000' of elevation. When I tore mine apart, it was clean...

On the other hand, I have a friend who's engine showed less mileage and had stock jetting. He ran 10w40 synthetic and non-synthetic oil, his piston and head had a severe coat of carbon build-up. His bike always smoked on decel until the last oil change when I talked him into trying 20w50 for test purposes.

If you're jetted reasonably close, take a look at the oil you're running. Don't run 10w40 or lighter oil.

 

Hey Gabe, Thanks for the fast reply.

I think I am jetted pretty close except for pilot if anything a little lean (160 main, WB pipe, K&N) everything else stock. I am running synthetic (not for the first two months) 10w-30 maybe to thin. I should probably go a little thicker at least 40w?

The last day I rode before my shifter fork broke, I could smell burning oil, but it wasn't smoking. I let a friend ride it with me following and I could really smell it bad.

I am sending the head off somewhere (suggestions? XC and HS racing) to have new guides, valve job and valves, and porting done. This is probably where the problem is, but I am not sure. Sending it off anyway while I have the cases split.

Nick Adams

 

Yes, I'd run a heavier oil.... The EX runs a much higher oil temp than a liquid cooled engine, so you have to run heavier grade oils if you want them to hold up. My friend was running Klotz synthetic 10w40 (very good oil) for most of it's life so far. Even it wouldn't hold up. He will run heavier grades as soon as he puts his engine back together.

I run 15w50 year round. I give my bike a good warm up period though.

I'd talk to GT Thunder on your head work. Have him do his "play porting", it will only cost about $50. Any more extensive porting will cost quite a bit more and yield very little gain, even on a heavily modified engine. The EX port design flows pretty well stock & really just needs a little clean up work.