Help me if you can

[ccriders]

I'm having a problem with spark plug fouling.
My first indication of a problem was the engine would start running roughly after about 30 minutes or so. I checked and cleaned the spark plugs at that time. They were some what black, but not grossly. A little research told me the fouling could be caused by exhaust back pressure, which could be caused by a collapsed exhaust hose. I replaced the hose and cut up the old one finding no damage (after 40+ years of use). Everything ran just fine.
Last year I replaced the carburetor as the old one started leaking gasoline. At that time I replaced the spark plugs gapped at .035. The new carburetor did not have an adjustable main port and soon there after I experienced the stalling and shut down. So I ordered an adjustable main port for the carburetor and cleaned the spark plugs. I think I have the carb set just right easy going, not too rich.
This past Monday I was motoring down the ICW, had gone about 8 miles and the stalling happened again. When the engine died, I put out the jib and sailed the remaining 12 miles back to the marina, which was quite nice. As I entered the marina I attempted to start the engine to no avail, so everything else was by sail.
Yesterday I put in new spark plugs and the engine started on the first go.
So now I have new plugs, new adjustable main port and an almost new carburetor, not to mention an almost new exhaust hose.
Anybody have a good idea of what is going on and how to proceed from here?

[JOHN COOKSON]

Do you have points or an electronic ignition?
Also do you have a mechanical or electronic fuel pump? The OPSS can fail in a weird manner at times.
Try running with the fuel fill cap loose to see if the tank vent is blocked.
Others will be along with more ideas.

TRUE GRIT

[roadnsky]

The new carburetor did not have an adjustable main port and soon there after I experienced the stalling and shut down...
I checked and cleaned the spark plugs at that time. They were some what black, but not grossly...
I think I have the carb set just right easy going, not too rich.

All of the plugs or just some?
Black plugs are not necessarily "fouled".

Can you tell us a bit more on what you did to "set" the carb?

Also...
This may be a fuel SUPPLY issue as John hinted.
What fuel filters do you have?

Last question...
When it died, was it sudden like turning off the key? Or stumbling, chugging, die.

[ccriders]

Electronic ignition.
Electric fuel pump.
What is OPSS?
After it died the last time I loosened the fuel cap, but still would not start.
All of the plugs looked the same. The bottom electrode was black, but not velvety with soot. The firing electrode looked normal.
When I installed the adjustable main port I followed the instructions closely. The final step was to close the port until the engine sputtered and then backed off a half turn. So it is about as lean as possible.
Every time it has died it's been a hesitation, loss of power, death.
I use a water separating main filter and then a 2 micron filter between fuel pump and carburetor.
The fuel tank was installed in 2006 with all new lines and filters. The 2 mc filter replaced a couple of times, a year ago last time as well as the main filter.
What I find interesting is that after every stoppage, I either cleaned or replaced the spark plugs and everything went back to normal. Clean crisp starting, very little smoke out the exhaust and only for a few moments when cold, then only clean water and no smoke. Electronic ignition is very impressive for quick and easy starting.
Thanks for your responses.

[ndutton]

Interestingly not a single mention has yet been made about checking for spark at either the time of shut down or no start.

OPSS = Oil Pressure Safety Switch, a normally open oil pressure activated single pole switch in the power feed to the electric fuel pump. It is USCG required to be certain the fuel pump is disabled when the engine is not running. A failure of the switch or its connections will stop fuel pump operation.

[JOHN COOKSON]

Then I Will

Interestingly not a single mention has yet been made about checking for spark at either the time of shut down or no start.
.

CC:
Next time there is a shutdown or a no start check for spark.
This will tell us which system - fuel or ignition - has the problem.

TRUE GRIT

[Administrator]

CC:
Next time there is a shutdown or a no start check for spark.
This will tell us which system - fuel or ignition - has the problem.

TRUE GRIT

+1.

Start at the top of the fault analysis tree.

Bill

[ccriders]

Would it be of any value to test the old spark plugs?
Seems every time there is a shut down it is very inconvenient to start fault isolation. This last time I was in the ICW with an ocean going tug coming right at me so I was quite busy getting the jib out (thank you roller furler!) and getting into the right place for a safe passing. Then it was time to turn into the ship channel behind a double barge and push boat, get the main up for better control, then passing an outgoing fuel tanker. When I finally got out of the ship channel I only wanted to sail on in peace and worry about the engine later, silently hoping it would start up later. Thanks for your inputs. If only I could have a shut down in the slip.

[JOHN COOKSON]

Would it be of any value to test the old spark plugs?
.

IMO testing the old plugs would be a waste of time.
If you feel compelled to keep guessing (could it be this?), rather than proceed with a trouble shooting plan, try looking under the distributor cap.

TRUE GRIT

[ndutton]

Seems every time there is a shut down it is very inconvenient to start fault isolation.

It may help for you to have able crew for sailing the boat while you get after engine failure diagnosis or vice versa. You may also want to visit the MMI online catalog for this:

https://moyermarine.com/product/the-engine-warning-and-diagnostic-system-ktas_01_564/

It doesn't cover everything but it's a big step in the right direction.

[thatch]

The easiest way that I can think of to check for spark, is to place a "fifth" spark plug on top of the motor and plug any of the four plug wires onto it and then have someone crank the engine over while watching it. If there is no spark, the ignition system is in "failure mode". You can also move from plug to plug to compare the quality of each individual cylinder's firing capability.
Tom
P.S. I keep a plug sitting on top of the alternator mount for just this purpose.

[CajunSpike]

What about temporarily installing one of those spark plug testers you leave installed inline...that flashes when it sparks?

Don't have to add/remove anything to follow progress while its running/failed.

[capnward]

Diagnose, but go ahead and grasp the straws anyway.

Definitely, check for spark to begin with, but I suspect your problem is fuel related. That to me is the usual problem. The engine ran fine for 30 minutes, then hesitated and shut down, which to me indicates a fuel issue. Cleaning the plugs may seem to temporarily fix the problem, but just shutting down the engine long enough to clean plugs may have the same effect. It may be that your plugs were fine. Drain your water separator to see if it has a lot of water in it. Once they get full they just send water into the carburetor. You replaced the carburetor because it leaked. It may have had a crack in the aluminum (unlikely), or it may have been caused by a leaking gasket, or junk in the float valve. Removing and cleaning carb and jets is routine for us A4 owners, in my experience. There may be a problem with your electric fuel pump. I have a mechanical one. It doesn't need an OPSS. A fuel pressure gauge between the 2 mc filter and the carb can tell you if there is a fuel restriction. Since you have EI, you might gap your plugs at .04 instead of .035. This might help the fouling.
Allow me to describe how I take care of my (usually) reliable A4. First I use MMO religiously in the oil and fuel, and use non-ethanol gas. In the spring I try to clean the carb and jets (new gaskets), replace water and inline filters, replace cap, rotor, and plugs, and oil the advance mechanism under the breaker plate in the distributor.. Every two years I replace water pump impellers. These parts are relatively inexpensive. I like to think of this as being pro-active, to deal with issues before they occur. Others may call it guessing, and say I'm wasting money on new parts I don't actually need. I realize the rational, systematic, scientific way is to wait until something goes wrong, then proceed down the diagnostic ladder one methodical step at a time. This way you learn your engine and systems. However, since I rely on my A4 for income, I can't afford to be shutdown while I sail back into the slip and diagnose, so I err on the side of preventative maintenance.
Most of the time this method works for me. In April this year, after the A4 sitting all winter and not starting, I replaced the coil, because spark wasn't as strong as usual. I tried testing it but my multimeter was faulty, I found out later. The old EI module, cap, rotor and plugs were all replaced, and probably didn't need to be. This is what they call grasping at straws. Then I noticed rust around the top of the coil, so I replaced it. Spark improved, but it still wouldn't start until a little gas was poured into the air intake, for lack of starting fluid. It's been fine since. Some weeks after I removed the old coil, I discovered it was leaking. I was guessing, but it turns out I guessed right. Sometimes you get lucky. Next time I'll have a working multimeter.

[ccriders]

So, where do I find this "diagnostic ladder"? Or "fault analysis tree"?

[zellerj]

How about using one of these, that I just purchased based on a post by Neil.

https://www.banggood.com/Auto-Car-Test-tester-Ignition-Spark-Indicator-For-Spark-Plugs-Wires-Coils-Diagnostic-Tool-fit-p-1036195.html?cur_warehouse=CN

I put mine in the tool drawer in my boat. Should be easy to check for spark now.