Cylinder #1 carbons up

[Renegade]

I have had my A4 running perfectly for 9 years now. This summer we noticed a lot of soot from the exhaust on the stern after running a short period of time but there was no noticeable difference in the performance of the engine. I have installed the pertronix distributor and ignition with the matching coil, electric fuel pump, all from MM. In addition, I installed the PCV valve and oil filtration system from Indigo. I use Auto light 86 plugs, Atomic 4 wires from Westerbeke. I changed the rotor and cap, the plugs gapped at 030 and the wires and no change. All the upgrades have been on the boat for several years.

The compression on all cylinders is 110 cold and 105 warm. On the advice of a mechanic, I added some oil to cylinder #1 and cold the compression only went up to 115. My under load, maximum RPM is 2000 and cruising at 6kts about 1800 seems to be the sweet spot where the engine is happy. The engine runs at a temp of 160 to 170 in the summer and 120 to 140 in the spring and fall. There is no noticeable oil consumption between oil changes.

I follow the MM maintenance recommendations faithfully including using MMO in the gas and oil. Any ideas? I'm at a loss

[joe_db]

#1 as in the front of the engine?
Usually it is the other end that does that.

[Renegade]

yes the #1 front cylinder.

[roadnsky]

IMHO all of your "numbers" seem just fine.
Still not understanding the mechanic's logic in adding oil to the cylinder tho

Here is a suggestion from one of our guru's (Dave Neptune) that might help with the soot...
"I have been gapping my plugs at .038~040" (larger gap acts a bit like a hotter plug)
Take advantage of the EI by opening up the plug gap a bit .040"

[joe_db]

IMHO all of your "numbers" seem just fine.
Still not understanding the mechanic's logic in adding oil to the cylinder tho

Here is a suggestion from one of our guru's (Dave Neptune) that might help with the soot...
"I have been gapping my plugs at .038~040" (larger gap acts a bit like a hotter plug)
Take advantage of the EI by opening up the plug gap a bit .040"

If you add oil and do a compression test, the number goes up if the rings are leaky and don't change if not

[roadnsky]

If you add oil and do a compression test, the number goes up if the rings are leaky and don't change if not

Ahhh, I get it now.
I mis-understood what he was doing. I thought he was adding oil to deal with the soot.
Gotta stop posting before I've had my coffee!

[tenders]

This engine sounds perfectly fine to me. If you're getting a bit of soot on the stern, maybe the carb is running a little rich?

Or maybe just forget about it? It probably starts very easily.

[thatch]

If you have added a pcv system, can we assume that you have an adjustable main jet? If so, you may want to lean out the carb a bit more.
Tom

[Renegade]

If the mixture was too rich, would it not affect all the cylinders? Also it's not the soot on the stern i'm concerned about. It's that something has changed and the spark plug is completely covered in black velvet. (soot). So even though it still runs, it's not running as it should.

[JOHN COOKSON]

Weak Spark Plug?

Try swapping the spark plugs around to see if the problem follows the suspect plug to a different cylinder.

TRUE GRIT

[thatch]

Normally all of the plugs will burn a similar color which should be a medium brown.
In your case, where one is way out of whack, I'd probably start by replacing just that plug, or by cleaning and swapping it with one from another cylinder. Another possibility could be a deteriorated spark plug wire. If you still have the old set you could borrow one from it. One item that is often overlooked is the spark arrestor, which will gradually become gunked up and reduce the system's air flow. Because of the PCV valve's job of removing oily air (blow-by) from the crankcase, they are also prone to becoming dirty. If it sticks in the closed position, it will definitely richen the mixture.
Tom

[roadnsky]

...Because of the PCV valve's job of removing oily air (blow-by) from the crankcase, they are also prone to becoming dirty. If it sticks in the closed position, it will definitely richen the mixture.

Excellent point Tom!

All the upgrades have been on the boat for several years.

Have you changed the valve since it's installation?

[Renegade]

I've gone through multiple plugs and wires but have not changed the PCV valve. I will try that. Spark is good. Only one cylinder is fouling so I doubt it's the mixture.

[edwardc]

Don't forget to check the inside of the distributor cap. A buildup of dirt can provide a path for the spark energy to arc to one of the other plugs, diminishing the spark on that plug and causing it to foul. This kind of problem usually leaves a spiderweb-fine track of carbon in the cap where the arcing is occuring.

A new cap & rotor is all it takes to fix.

[ndutton]

Remember that fuel/air system issues are not cylinder specific while ignition issues can be. The comment discounts mechanical cylinder problems.