help - head off and carbon build up

This may be a real easy question but I need some quick advice -

I had a tapping sound which I assume was a lifter so I prceeded to replace them with new ones and when I pulled the head I noticed that the 4 5 & 6 cylinder had an excessive amount of carbon on top of the piston and the 1 2 & 3 were very clean. this engine only has about 1200 miles on it and has had no noticable problems other than tapping sound.

Can anyone give some suggestions on what to look for or what to do to cure this.

thanks

Mike

Where is the carbon located on the piston? center only? round the edge? just one side? Is it dry and dusty or wet/greasy?

ChukM

Carbon is on entire piston and around valve openings. It is dry and flakey
NOt stickey. 12& 3 cylinders have no carbon. I am in process of replacing valve stem seals but have had no problem with smoke.

:roll: good question. i don't know the answer but had a head i pulled at 300 miles and it had 5 cyls. smoked black. the #4 cyl. was as shiny as new. i never found a reason for this. maybe if you get an answer to your question then it will help me with mine...frank..

You didn't mention which carb you have, but here's some experience:
if you have the Holley 1946 (circa late 1970s) or have added a 2-bbl on the log head, they could be leaking fuel from the power valve. The 1946 is famous for this because it tends to warp the top piece, especially if the heat riser coil in the exhaust manifold corroded away long ago, causing overheating of this upper plate. The warped gasket surface then cannot hold the vacuum well enough to lift the power valve shut all the way, so it leaks.

The 2bbl carbs need a different spring in the power valve because the manifold vacuum runs lower than it would on a V8, where it probably came from. In both cases, the engine usually runs fine, but the rear cylinders collect the gas, particulary when parked, causing the carbon buildup.

Finally, check for a worn-out float needle while you have it apart. Better still get a rebuild kit and try it real quick. If it fixes it for a while, then goes bad again, that's your clue.

I have a Carter YF carb - don't know exact ID for it - but have had leaking problems with it - this could be my problem - I've never noticed any interior leakage but have had external leakage when car is parked.
I'll check and see - just put new gaskets in carb. maybe that is the answer. Have you had any experience with YF's and if a different spring would work or maybe just a new base?

Thanks

Mike