Carbon fouled exhaust valves?

[Lirker]

So I took my headers off yesterday to paint my block, and I saw that two of my valves (Valve 2 and 4) were carbon fouled. Valve 4 has a light film of carbon on it, while valve 2 has a heavy coat of carbon. I knew I would have to address this soon, because when I pulled my second spark plug it was heavily fouled with carbon, while all the others were okay. So my question is; what causes this? Is it the air/fuel ratio causing this?


What's the best way to clean the carbon up and fix this issue?

I had pretty normal idle, and functionality when my car was running. I also changed my AFM to what seemed a good stock untouched unit with the blue cap still over the hex bolt where you adjust the ratio.
Also, the head was rebuilt about 5k miles ago, with new valve seals. This is why I believe it is the A/F ratio. Any help is appreciated.

[Ether-D]

My guess is a stuck open injector or two. Clean or swap in known working ones.

[Lirker]

My guess is a stuck open injector or two. Clean or swap in known working ones.

Makes sense, because the only thing I haven't swapped in the engine bay are my injectors! Any tips on cleaning the valves? Break cleaner?

[jeffnhiscars]

The risk of dislodging a chunk of carbon with subsequent damage is very real. All,it takes is one small chunk stuck to a valve face and you have one burned valve. If it passes in to the cylinder you risk scoring a wall.

Other than removing the head, your best bet is to make sure your injectors and ignition system are 100% (so plugs, injectors, valve adjustment, cap etc) then take it for a good blast on the highway. I'd throw in a fuel additive for good measure and see where you wind up.

FYI that block shows signs of a leaky head gasket. Perhaps thats from before you pulled the head but if not you may be pulling it again which would give you the chance to decarbon.

[MR E30 325is]

Makes sense, because the only thing I haven't swapped in the engine bay are my injectors! Any tips on cleaning the valves? Break cleaner?

A great way to clean carbon buildup in the combustion chamber and its components is to do a stint on the freeway in 3rd or fourth gear (depending on your diffs final drive).

Every now and then I will sit in 4th at about 4k rpms and drive 10 ish miles. I don't have any testing information, but the engine always felt better afterwards.

[Supratreo]

There really is no way of getting the carbon off the back of the exhaust valve other than a wire brush or blasting it Like they do on the new DI cars.
Doing a pull on the freeway really only keep the combustion chamber clean and you should do that every once in a while.
And only thing I would really worry about if carbon breaks off is clogging the cat, chances are it will leave the cylinder before it can do any damage, but with the header I'm assuming you don't have cats.

I think the best thing,to do is remove the head and clean it up if it's a big issue, which I don't think it really is.

[digger]

In a running engine get the Subaru upper engine cleaner or Seafoam