Atomic 4 dies a few minutes after engaging transmission

Jul 12, 2021
20
Pearson 32 Winthrop Harbor
I have a 1979 Pearson 32 with an Atomic 4 engine. On a recent trip we motored for about 30 minutes when we started losing power and the engine died. It seemed like it had run out of gas, but that wasn't the case, the gauge read 3/4 a tank of gas. The engine started back up and ran normally. We engaged the transmission and it ran fine for another 10-20 minutes before losing power and dying again. We disengaged the transmission and started the engine back up. After engaging the transmission again it ran for another 10 minutes. Each time we did this it ran for shorter and shorter amounts of time after engaging the transmission.

I didn't have any lines go missing so it's probably not a wrapped propeller. The appears to start and idle okay (it's turned up a little too high). While the engine does occasionally cut off when moving, it's usually at low speeds, I can't remember it ever cutting off at higher speeds.

Thoughts?
 
Feb 10, 2004
3,520
Hunter 40.5 Warwick, RI
I had a A4 in a 1968 Morgan 30 that exhibited similar run issues.

Recheck the prop for wrapped lines or debris. You could have picked up a piece of floating line.

By all means check or replace the fuel filter.

My fuel tank was mounted above the engine so it had an anti-siphon valve. If this applies to you, check that valve for proper operation.
I rebuilt the fuel pump thinking that it did not have enough output pressure. I think that helped. IIRC the pressure should be 7-10# at the carb input.

My understanding is that up-draft carbs are nororious for issues. But that is the design and it should work if everything is OK.

I had a lot of running problems with this engine. It was 30 years ago and I can't remember if I solved all of the problems or not. But I remember that it drove me crazy.

Good luck.
 
Jul 12, 2021
20
Pearson 32 Winthrop Harbor
Ok, thanks. Do you know if the engine and the transmission share the same oil. My gut tells me they do, but I haven't touched the back of the engine.

My tank is at the same level as the engine, but it pulls gas from the top. I think anti-siphon refers to the lock on the take that I can hear click off when I turn the key to provide power.

It does feel like something may have gotten wrapped, maybe it got tighter and tighter making run time shorter and shorter. I wonder if a thin line could do that, like a fishing line....

What are up-draft carbs?
 
May 17, 2004
3,539
Beneteau Oceanis 37 LE Havre de Grace
Is there any kind of fuel tank vent that may be closed or clogged? Running for a period of time then stopping would be consistent with a partial vacuum forming in the tank.
 
Jul 12, 2021
20
Pearson 32 Winthrop Harbor
I don't know of a vent like that. I could just open the gas cap to test the theory. However, it only happened when the transmission was engaged.
 
Feb 10, 2004
3,520
Hunter 40.5 Warwick, RI
Ok, thanks. Do you know if the engine and the transmission share the same oil. My gut tells me they do, but I haven't touched the back of the engine.

My tank is at the same level as the engine, but it pulls gas from the top. I think anti-siphon refers to the lock on the take that I can hear click off when I turn the key to provide power.

It does feel like something may have gotten wrapped, maybe it got tighter and tighter making run time shorter and shorter. I wonder if a thin line could do that, like a fishing line....

What are up-draft carbs?
I believe that the engine and transmission do share the same oil. At least I don't remember changing the transmission oil separately.
The anti-siphon valve may not apply to you since your tank is at the same level as the engine. The anti-siphon valve I am referring to is a spring-loaded valve the only opens when the fuel pump is pulling a vacuum and drawing fuel. Thus you need a fuel pump that pulls hard enough to open that valve. A small air leak could cause the valve not to open fully.

By all means test for a vent problem by opening the fuel fill to the tank. That is an easy test and it can eliminate looking at a bunch of potential problems.

I don't think a small line could cause the engine to stall and quit. This is probably not the problem because a wrapped line would bind the engine immediately in gear, not after 10-20 minutes.

Up-draft carbs are those where the air enters the bottom and the intake manifold is connected to the top of the carb. Some engines like the A4 used them but they were not popular in later designs.
 
Aug 28, 2006
499
Bavaria 35E seattle
Trans oil is the same as the engine on an A4. Otherwise, I'm stumped by your stopping problem other than the fuel filter as mentioned before.
 
May 9, 2020
57
Hunter Legend 37 Harrison Twp, MI
My A4 would quit after 10-15min, then not always restart until 20min later... turned-out it was the coil. As they get bad, running at power (trans engaged) and heat-up, the problem comes. Cools down, works. Your issue doesn't sound exactly the same, sounds like you can restart right away, but if you haven't changed your coil lately, change it or get carry a spare. It will go eventually! Not sure if SBO carries them, if not can get one at NAPA.

Recommend posting on the Atomic 4 Forum at Moyer Marine. They are really helpful and will help you troubleshoot knowing the common issues with A4s.
Moyer Marine Forum

Note to SBO - sorry to direct to another forum, but it's dedicated to the A4, and the expertise is concentrated there. Hope that is ok! I am not affiliated with them at all, and only recommend the forums for troubleshooting A4s.
 
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Jan 1, 2006
6,160
Slickcraft 26 Greenport, NY
I had an A4 in my Ranger. I had a similar stalling problem. I suspected a contaminated fuel tank. I tested it by hooking up a clean outboard motor tank to the fuel intake. I found the stalling stopped. So I took the Ranger's tank to a radiator shop to have it cleaned out. Somewhere in there, I rebuilt the carb and the fuel pump. No more problems. I had the Zenith carb, and I'm not sure about the "Up draft" issue with that. I don't think there was an anti siphon valve. The tank was above the engine to some degree.
 
Jan 18, 2016
695
Catalina 387 Dana Point
An A4 is basically 4 briggs&straton lawnmower engines stuck together. 1930's technology. Suck, Squeeze, Bang, Blow. Engine runs so compression should be OK (squeeze). Blow is the same, I wouldn't assume any exhaust issues.

#1: Fuel. Running at power the engine needs more fuel. So a mediocre fuel pump, filter, carb, air leaking into a fuel line, etc will cause stalling. My A4 had these symptoms when the carb was gummed up and when the fuel pump started to die. Big clue here (as I read it) is it runs OK for a bit (carb bowl draining).

#2: Spark: Could be a bad coil, points getting out of whack when heated, etc.. Electronic ignitions are significantly more reliable than points/condenser.

I'm guessing fuel pump. Weak pump or bad wiring/oil press sender(if electric) The portable tank test gravity feeding into the carb is a good way to rule out/dx pump/filter/tank issues.

If'n you have the original engine-driven fuel pump, I'd replace it with an electric one. When the diaphragm goes bad on the mech one it can leak fuel into the oil.
 
Jun 2, 2011
345
Hunter H33 Port Credit Harbour, ON.
My Buddies Catalina 30 has the A4 and his would suddenly quit. It wouldn't always start right away but always would eventually. The problem was a defective oil pressure switch which, when warm / hot, would either close or open up. (Cant remember if it was normally open or normally closed) The switch is in the ignition wiring and is a safety shutdown if you loose oil pressure. Found a new switch at an automotive store.

Maybe yours has the same switch.
 
Jul 12, 2021
20
Pearson 32 Winthrop Harbor
I had an A4 in my Ranger. I had a similar stalling problem. I suspected a contaminated fuel tank. I tested it by hooking up a clean outboard motor tank to the fuel intake. I found the stalling stopped. So I took the Ranger's tank to a radiator shop to have it cleaned out. Somewhere in there, I rebuilt the carb and the fuel pump. No more problems. I had the Zenith carb, and I'm not sure about the "Up draft" issue with that. I don't think there was an anti siphon valve. The tank was above the engine to some degree.
Interesting. Thank you. Removing the tank would be a nightmare, but I wouldn't be surprised if it was dirty. I wonder how I can check this without removing.
 
Jul 12, 2021
20
Pearson 32 Winthrop Harbor
My A4 would quit after 10-15min, then not always restart until 20min later... turned-out it was the coil. As they get bad, running at power (trans engaged) and heat-up, the problem comes. Cools down, works. Your issue doesn't sound exactly the same, sounds like you can restart right away, but if you haven't changed your coil lately, change it or get carry a spare. It will go eventually! Not sure if SBO carries them, if not can get one at NAPA.

Recommend posting on the Atomic 4 Forum at Moyer Marine. They are really helpful and will help you troubleshoot knowing the common issues with A4s.
Moyer Marine Forum

Note to SBO - sorry to direct to another forum, but it's dedicated to the A4, and the expertise is concentrated there. Hope that is ok! I am not affiliated with them at all, and only recommend the forums for troubleshooting A4s.
Thanks! I actually found a great video from Moyer Marine on this topic:
 
Jan 1, 2006
6,160
Slickcraft 26 Greenport, NY
Interesting. Thank you. Removing the tank would be a nightmare, but I wouldn't be surprised if it was dirty. I wonder how I can check this without removing.
If you use gas with alcohol your tank can be contaminated. Mine was relatively easy to remove.
 
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Jan 18, 2016
695
Catalina 387 Dana Point
If you suspect the tank, run the motor off of an outboard tank to test.

If you suspect ignition, as Moyer says in the video, test while the motor has stalled. I normally would use the shadetree "hold the plug wire close to the block an look for the spark" technique, but neon spark testers are widely available for ~$5. You can leave it in so that if it stalls run down and look.

I'm still betting a doughnut it's fuel.
 

DArcy

.
Feb 11, 2017
1,301
Islander Freeport 36 Ottawa
The A4 in my C&C 27 did this for a while. My fuel filter was constantly getting clogged up. I was able to look inside the tank by removing the fuel sender. It turns out the fuels sender was the problem. It had rotted out and the debris and corrosion from the sender were sitting in the bottom of the tank. I could not get it out through the hatch so I used a Pella oil extractor to suck all the debris from the bottom of the tank which fixed the problem.
Running off a portable tank for a while to test the theory is also a great idea if you can't look into the tank.
 
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