Excessive Carbon???

[andy6374]

Background:
88' 200hp V-6 blackmax


Engine has sat idle for the past 22 months during a boat resto.

What I've done prior to attempting to set sail:
-Rebuilt fuel pump, cleaned carbs, new fuel lines, primer bulb and fuel filter.
-New waterpump, tstats and poppit assembly.
-And all the other stuff you'd normal do at the begining of a season.

At any rate, the spark plugs on my #1 and #2 cylinders get caked I mean caked with black soot...looks like carbon. The other cylinders are fine. I clean it off and it comes right back. It is keeping the engine from idling down. I have spark on all cylinders and 110 psi on all cylinders

Question:
Will just a heavy decarb do the trick? Is it just carbon? Before the boat was laid up (2 years ago) I decarbed the engine but never ran it the stuff out because of another problem that is now solved. When I first ran the engine the other day a piece of carbon the size of 2 silver dollars got caught between the prop and L/U.

What do you guys think? If it is carbon soot on the plugs, I've never seen it so bad.

 

[tmcalavy]

Re: Excessive Carbon???

Sea Foam...in the spray can to spray into the carb while running, in the can to mix with a fresh batch of fuel. Can't beat it.

 

[andy6374]

Re: Excessive Carbon???

tmcalavy-
Yeah I know how to decarb, but do you think it IS excessive carbon build up. Why only on the top cylinders on each bank (1&2)? It's just wierd, done dozens of tune-ups (and decarb's) but never seen crap like this.

 

[Silvertip]

Re: Excessive Carbon???

You probably have a carb that is running those cylinders way rich. When you say you cleaned the carbs, was that a total disassembly, soak, blow out with compressed air and reassembly with new kits? If not, you need to. Float level set too high, hanging up, needle and seat sticking, etc.

 

[andy6374]

Re: Excessive Carbon???

Silvertip-
The carbs weren't rebuilt (with the $100 kits) just disassembled, soaked in marine carb cleaner, blown out with compressed air and then reassembled with new gasket kits (~$7).

I'll check float levels etc... It's not leaking fuel out of the carb when I pump the the primer bulb hard, so it can't be set too high. I usually errr on the side of caution and set them a hair too low. But I definitely agree something isn't right. The fact that it's the two cylinders that is being feed by the top carb speaks volumes. I guess I was anti-carb problemo because I just cleaned them but then again it wouldn't be the first time someone messed up.

-andy

 

[j_martin]

Re: Excessive Carbon???

Put a moderate squeeze on the primer bulb while looking in the carbs. If a needle is giving trouble, that hole will flood.

A bone crushing grip on the bulb will make a good one fail.

hope it helps
John

 

[andy6374]

Re: Excessive Carbon??? Update 7/3/07

Re: Excessive Carbon??? Update 7/3/07

Checked the carb today...no problem there.

The floats are set to 1/16" spec and if I blow on the fuel intake I can't get any air in there. So the seat is seated as well as the needle.

I might mention that is soot buildup, it's not a wet spark plug situation.

Still can't figure it out. Could I have spark, but weak spark on those two cylinders

 

[andy6374]

Re: Excessive Carbon???

Any ideas? I'm stumped.

Anything else to check. Only the top two plugs keep getting fouled with carbon.

 

[j_martin]

Re: Excessive Carbon??? Update 7/3/07

Re: Excessive Carbon??? Update 7/3/07

Checked the carb today...no problem there.

The floats are set to 1/16" spec and if I blow on the fuel intake I can't get any air in there. So the seat is seated as well as the needle.

I might mention that is soot buildup, it's not a wet spark plug situation.

Still can't figure it out. Could I have spark, but weak spark on those two cylinders

Yes, you could. would be a bad trigger. Low odds, though.

John

 

[andy6374]

Re: Excessive Carbon???

Update:

I took off the bleed lines, one by one, and blow them out with compressed air. Put the lines back on and the check valves seemed operational, that is I could suck but not blow or vise versa.

However this didn't fix the problem.

Then today I bought 2 new needles/seat kits. The motor seemed to idle much better. However the plugs were still sooty.

Did you think that this was just some leftover deposits from all the rich running those cylinders have been doing?

 

[Smig]

Re: Excessive Carbon???

Andy,
There may be left over soot that has to be cleaned out, have you tried decarbing it since you replaced the needles?

Just wildly guessing here - did you check the spark on those cylinders? or maybe there is an intermittent miss - just enough to leave to much fuel in the cylinders?

Sorry I don't have anything more solid for you.
Smig

 

[andy6374]

Re: Excessive Carbon???

Tried to take the boat out today with no luck.

Still fouling those top two plugs. They have spark and good compression...I'm at a loss. Probably going to end up taking to a Merc dealer, unless anyone can think of some other stuff to try.

 

[Smig]

Re: Excessive Carbon???

Here's another wild guess:

You mentioned poppits and thermostats - any chance there is something wrong in your cooling loop and those two cylinders are running cold (or hot - I think one of them causes fouling?)

Also, when you say "no luck" do you mean more fouling or the engine is not performing at all?

 

[andy6374]

Re: Excessive Carbon???

Just those two are fouling. The rest are fine.

The engine is getting up to temperature. Just so you know it's excessive cooling that fouls plugs.