1974 a4- randomly stalls while cruising

[Gubernaculum]

Hi folks,
I have a new-to-me a4 - an original 1974 a4 in my c&c sailboat. Never rebuilt, all Great Lakes freshwater till now, unknown hours. Good oil pressure.

I bought the boat and have been making my way down the icw, about 200+ miles so far. When it runs it runs great, but every now and then it will stall, which is disconcerting to say the least. So far it has restarted each time afterwards but more recently it is taking longer and longer to restart. Stalls tend to be at what I think is cruising speed- no rpm/tach, but usually at 4.9 knots with 33ft boat and max prop. I've run a good bit of gas thru it motoring the icw, so I don't really think it's old gas.

Cold starts take 3 or so 10-second cranking attempts to start up. Warm starts fire right up.

Supposedly the last service was in July. Plugs and wires look good. I just replaced the external racor fuel filter/separator.

Any suggestions about where to start with diagnosis? Is this a typical issue?

[Oldlaxer1]

First question, mechanical or electric fuel pump?

[Marian Claire]

Welcome to the forum.
Is the stall a stumbling slow shut down or a sudden stop as if the key has been cut off?
Dan S/V Marian Claire

[joe_db]

The most common issue is the coil is going bad. If this is so, it will get worse and worse.

[Gubernaculum]

It is more of a sudden cut off, which was weird to me. The first few times it restarted immediately, but the more recent stalls have taken several attempts to get it going again. This has happened two to three times per day while motoring the ICW.

Mechanical fuel pump I believe. I will add a coil to my shopping cart - it would be smart to carry a spare anyway.

[joe_db]

Do yourself a favor and get the Moyer Marine coil. TLDR; It is the end result of a fair amount of research into coils and which ones last the longest. Plenty of coil threads if you need details.

[romantic comedy]

What would I check?

Is the gas tank vent clogged? Or any other fuel flow obstruction, like an intermittent filter.

Fuel pump intermittent? That happened to me with the Atomic Four. But it was not a sudden shut down, but it ran erratic before stalling.

Is there something that could be blocking air flow to the carb? Unlikely..

Is there an ignition wire that is grounding somewhere. A pinched wire? Take off the dist cap and look at the wires and connection? wiggle and look for a short possibility.

I might hook up a by pass wire direct from the battery to the coil. That bypasses the ign switch and wiring. And bypasses the oil pressure switch.

[JOHN COOKSON]

It is more of a sudden cut off, which was weird to me. The first few times it restarted immediately, but the more recent stalls have taken several attempts to get it going again. This has happened two to three times per day while motoring the ICW.
I will add a coil to my shopping cart - it would be smart to carry a spare anyway.

Do you have points or an electronic ignition? If you have an electronic ignition the present coil may not have enough resistance and be overheating due to the longer dwell that comes with an electronic ignition. Coil heat damage is progressive until the coil fails entirely. You can read all about it in the "coil threads" Joe mentioned.
Here's something that might work: When you have a shut down quick, quick before the coil has a chance to cool off, go down below to the engine and pull the big center wire out of the coil and hold it near ground (the engine) then turn the engine with the starter to see if you have spark.
If the problem turns out to be the coil deep six it - don't carry it as a spare. Buy a new one. IMO a unreliable spare is no spare.
All this having been said keep in the back of your mind that there are parts of the boats electrical system that can fail in a progressive manner also. The way to diagnose this is to bypass the boats ignition circuit with a hot wire directly to coil +. A wire from the battery or from the big wire connection on the back of the starter motor would work. Do not leave this wire connected and hot when the engine isn't running for more than 30-45 seconds or the coil will be fried.
Once we're sure the ignition system is working correctly, if you are still having shut downs, we will look elsewhere - the fuel system. This is a systematic approach to trouble shooting. A systematic approach avoids jumping back and forth between possible causes - the nautical version of chasing your tail.

TRUE GRIT

[joe_db]

I think you meant pull it out of the distributor. The coil end needs to stay in
Also note coils on points systems can fail too.

Do you have points or an electronic ignition? If you have an electronic ignition the present coil may not have enough resistance and be overheating due to the longer dwell that comes with an electronic ignition. Coil heat damage is progressive until the coil fails entirely. You can read all about it in the "coil threads" Joe mentioned.
Here's something that might work: When you have a shut down quick, quick before the coil has a chance to cool off, go down below to the engine and pull the big center wire out of the coil and hold it near ground (the engine) then turn the engine with the starter to see if you have spark.
If the problem turns out to be the coil deep six it - don't carry it as a spare. Buy a new one. IMO a unreliable spare is no spare.
All this having been said keep in the back of your mind that there are parts of the boats electrical system that can fail in a progressive manner also. The way to diagnose this is to bypass the boats ignition circuit with a hot wire directly to coil +. A wire from the battery or from the big wire connection on the back of the starter motor would work. Do not leave this wire connected and hot when the engine isn't running for more than 30-45 seconds or the coil will be fried.
Once we're sure the ignition system is working correctly, if you are still having shut downs, we will look elsewhere - the fuel system. This is a systematic approach to trouble shooting. A systematic approach avoids jumping back and forth between possible causes - the nautical version of chasing your tail.

TRUE GRIT

[ndutton]

The first few times it restarted immediately, but the more recent stalls have taken several attempts to get it going again.

This is the typical overheated coil symptom. Do you find the run time is a little shorter before the next shut down? It's not guaranteed to be the coil however.

A fuel check at shut down is done by removing the main passage plug at the bottom of the carburetor bowl to see if fuel runs out (have a catchment under the carb). No fuel = fuel system problem.

An easy way to check the tank vent is to run with the fill cap open temporarily. No shut down = vent line is suspect.

[Dave Neptune]

G, if you have a point type ign A "cooked coil" is possible but not as likely as with an electronic ignition. A caution to you on this~~when checking the spark all that gives you is that you have spark NOW or not. If you have the std point type ignition try to hot wire the ignition to check the ignition circuit~seen to many loose wires, bad connections and worn out key switches. Pay close attention to the wiring circuit if you have a std ignition.
If you have an EI it can be in the circuitry but more likely the coil.

Another possibility is fuel starvation an easy check with the manual pump or with a pressure gage. NEXT TIME SHE STALLS REACH IN AND PUMP THE BAIL, if you pump fuel into the carb and then she starts you have found the problem in the fuel circuit.

Dave Neptune

[Gubernaculum]

Fixed!

Fixed! It was the coil. I replaced it with the Napa coil (I was short on time, couldn't wait for shipping), and had no more stalling over several days of running the ICW. It seemed to start up easier as well.

Since the boat was in another town and I wasn't sure if it had electric ignition vs points, I picked up a resistor. Now I figured out I have points/condenser but still have the resistor sitting around. Would there be any benefit (for coil longevity) if I went ahead and put the resistor on?

Thanks so much for the suggestions, folks! I had convinced myself it was a fuel issues - I wasn't even considering the coil. Considering the bad weather I was motoring against on the ICW over the last few days, a stall at the wrong time could have spelled disaster/grounding.

[ndutton]

Before adding the resistor, have you determined why the coil failed? Was the ignition left on without the engine running? Has there been an alternator problem causing a higher than normal voltage? Dare I ask, do you have a manually adjustable regulator? Has the dwell been to spec, not too high?

What size resistor do you have?

[Gubernaculum]

Very good points (thanks) - I'll have to double check dwell, charging voltage, etc, next time I go to the boat. No idea if the ignition was ever left on (boat is new to me).
The resistor I have is the napa ICR5500

[sastanley]

Gub, There should be NO need for a resistor, unless your boat is not normally rigged, like one of the reasons/conditions Neil mentioned above.

I would NOT add it at this time...additional components only further confuse the troubleshooting and elimination process.