Coked up intake valve tops

[motorheadted]

my 427 with @ 3000 mi  showed a lot of carbon fouling on the top side of the intake valves . visable looking thru the weber intake runners. I was tearing the engine down to replace the heads .  Don't know if the deposits were oil or gas deposits,  Tops of pistons had same type of fouling.  Replacement heads (e-brok ) were rebuilt w
/ viton seals.
 After about 400 miles , I pulled the intake to put the 4bbl on, and noticed the new intake valves were coked up just like previous, in only a few hundred mi.
Any body here have a n answer as to what might be going on here ?  I think I saw a comment some where about timing.  Also gasoline formulation ?
Tried the search function, but no help.
I'm running 93 oct.
I remember Shell advertising some years ago, that shell had an additive in their gas that  kept the valves clean . Don't know if that is current or not. 

Ted

[shady]

usually caused by blow-by. good quality fuel helps. maybe a pcv issue. do you run it hard every now and again? babying doesn't help. this is becoming a problem with direct injected modern motors because there is no fuel going thru the intake runners to clean the valves. Is the motor using oil?

[motorheadted]

Shady:  I'm going to get some better gas tomorrow, probably Shell 93,  have been using Racetrack mostly. I'm still carb tuning, as I recently changed from webers back to single Holly, so I' been running pretty hard. No oil burning that I can tell. Plugs look good.

[Stangman]

I had the same thing when I took the heads off the motor. Not sure why it was like that, my engine ran well not rich and not lean. I always used 93 or 94 octane and 110/112 at the track. Like a black build up.

[frnkeore]

Could we get pictures of the deposits?

Edit: Since you can see the deposit, from the intake side, of the manifold, are we actually, talking about what I call, the back side of the valve head and not the combustion chamber side?

When I was a mechanic, the normal cause of a heavy build up, with umbrella seals, was loose valve guilds. Intake guilds shouldn't be looser than .0025. So, I would check both the guilds and be sure your Viton seals fit the valve stems. But, I wouldn't expect, even at .003 that the valves would have a heavy build up, in such few miles. So I would check the ID of the guild and OD of the stem, too.

I would also check the fit of the intake gasket for any sign of leakage or misfit.

[GerryP]

One of the most common causes for that is excessive idling and cruising for burgers.  We like to hear our snotty cams and let others at the burger cruise enjoy it too.  If you run it harder like you would a daily driver, those problems are not quite as common.  If you do use the engine as it was intended, then you can look for mechanical issues like PCV, intake gaskets, valve guides, and stem seals.

[motorheadted]

Frnkeeore & Gerry ;  as far as the guides, seals, etc, it's all new/rebuilt.  "Excessive idling " is a very good possibiity , as I spent hours with the engine idling trying to get the webers  synced  and idling properly. Finally had to give up and put the 4bbl back on. 

[Joe-JDC]

New heads, same problem, look at the fuel delivery.  Bleed down after shut off engine?  Overly rich idle?  Too much idle time?   Joe-JDC

[6667fan]

What PCV system are you using?

[motorheadted]

6667; PCV valve in RH VC, hose to intake under carb. Also have oil cap vent on LH VC, and one on intake oil tube, and rear intake vent with hose goin to "puke tank" oil/air seperator which drains to oilpan.

[Hemi Joel]

Cams with lots of overlap combined with lots of low speed and idleing can do that. During the valve overlap, exhaust gases are pushed into the intake port and condense on the back of the valve because it is cold from the incoming charge.

[6667fan]

Sounds like vapors are moved adequately with the systems you have in place. If it is not consuming oil or fouling plugs there may not be a problem? I mentioned the same concern on a 427 I had  to a builder I worked with for 35 years and he said that such buildup is not uncommon. ( Of course he has seen so much, so often, that he does not have the same degree of worry about things inside an engine that his customers do).

[motorheadted]

hemi joel:   Valve overlap, excess idle time, crappy ethanol,  I'm going with those.  Thanks for all the input !