Carbon buildup and pitting!

[DesmoTillDeath]

Recently took the heads off to get the valve seats cut to find several interesting things.

1. exhaust valve head on horizontal cylinder was cracked.
2. Carbon buildup was substantial on heads and piston.
3. Found pitting in throttle body near butterfly valve.


IMG_3562[1] by yumaaz1987, on Flickr
Here's the vertical throttle body open. The white specs are pits!


IMG_3556[1] by yumaaz1987, on Flickr
Horizontal throttle body.


IMG_3564[1] by yumaaz1987, on Flickr
Vertical cylinder head! (Horizontal head looks the same)


This seams like an excess of carbon dont you think?
This m900 has 32500mi and I only run 91 in it. It has been back firing and running rough for a while now. Low compression as well. Hence the seat cutting.

Do we conclude that the pitting it from hot cheese blowing back up past the intake valve? A leak down test ended in a strong breeze out exhaust and intake.
Have not looked deep into piston slack yet but a visual and poking test concludes they are not sloppy in cylinder.

[Speeddog]

That looks like a bit too much carbon.

But.... depends how good (or not) the valve stem seals are.

And most 2-valvers do just fine on 87, 91 can produce more carbon.

Dunno about the TB pitting.

[DesmoTillDeath]

Speeddog: As soon as I swap in a used valve to replaced the cracked one, you will be seeing these heads for cutting.

We had talked about replacing the seals as well so maybe that will solve this problem.

[brad black]

the pitting is std, don't worry about it.

carbon looks wet, so I'd be thinking more oil than anything else.  excessive squish clearance can lead to it building up too, and lack of rpm in usage.  if there's no room, it's not there.