Where's the carbon from?

'82 KZ1000

See the carbon on the back of the intake valve, but none in the surrounding port. Where does that mean it's coming from?

Valve guide seals.
Steve

Valve hotter than aluminum port.
Shit ,( Fuel) and oil sticks to it and builds up
Chamber and piston dome probably covered too
Dave

Tune up in a can can't help the seals any.
Steve

Street Fighter LTD wrote: Valve hotter than aluminum port.
Shit ,( Fuel) and oil sticks to it and builds up
Chamber and piston dome probably covered too
Dave

So is it fuel or oil? If fuel, is the valve too hot, or air/fuel too rich. Tuned, ran fine, no black smoke.

And yes, piston/combustion chamber covered also.

You should have seen mine. 20 year old seals, ran like a scalded cat, puff of smoke on start up, fouled plugs every 400 miles. Installed Viton valve guide seals, clean as a whistle inside now. I put in new springs and valves too but that's because it was needed.
Steve

Seals are new. This happened after only a few thousand miles.

VTEC wrote:

Street Fighter LTD wrote: Valve hotter than aluminum port.
Shit ,( Fuel) and oil sticks to it and builds up
Chamber and piston dome probably covered too
Dave

So is it fuel or oil? If fuel, is the valve too hot, or air/fuel too rich. Tuned, ran fine, no black smoke.

And yes, piston/combustion chamber covered also.

Lots of variables in this answer

Hot many miles on motor ?
State of tune thru its life.
How long did it idle ?
Valve seal condition
What kind of fuel and what was in it ? Additives, Water , dirt, old fuel, and more
These motors and most others have deposits as a by product of combustion
Dave

How were the valve guides? Cheap seals can do it. Additives can too.
Steve

DO the old motor head trick and add water thru carbs to a hot running motor and give it throttle so it doesnt stall

then watch steam and crud fly out exhaust :whistle:
Not for the weak of heart
Dave

OK.
MTC 1075/10.5:1 kit
Head is ported to the max (too much) with APE oversized valves on OEM seats, bronze guides with Viton seals.
Street cams
FCR35 carbs (pods)
Kerker with 2" baffle
Only a few thousand on the engine.

Used nothing but clean 93 octane.

Tuning was a bitch and there was some hot idling, but nothing extreme. And again, only a few thousand miles.

Tore it down after pistons got scuffed on the thrust side above the top rings. MTC says it's from heat from the carbon.

Seen a lot of car engines burning tons of oil from rings, and the carbon build up is always on the back of the intake valves and all around inside the port from valve overlap. This is different, only on the back of the valves.

Wondering if the guide bores were scored when the originals were removed and the oil is going around the guides.

Street Fighter LTD wrote: DO the old motor head trick and add water thru carbs to a hot running motor and give it throttle so it doesnt stall

then watch steam and crud fly out exhaust :whistle:
Not for the weak of heart
Dave

I got it tore down already.

Sent the block out. I little too much clearance so I got another standard block to re-bore to a new set of pistons. Just want to cover all the bases before I put it together again.