Runs great, but stalls out under power

[Catfish]

My A4 starts right up, idles great, accelerates good, but after running under power for 30 to 120 seconds starts sputtering and dies. It'll start right back up, but repeats the stall after a minute or two when under power.

The prop is clear and turns freely by hand, I installed an ignition tune up kit (points, condenser, etc.), I've verified compression in all cylinders, verified firing order, bypassed the oil switch, bypassed my fuel tank and am using a portable fuel tank (checked that it was vented) with new fuel, even pulled a plug wire while running to see if the engine performance improved (it did not). The fuel pump is clicking and pumping fuel....I'm at wits end. Anyone have any suggestions?

[jcwright]

Hello catfish.

Others who are far better at remote diagnostics than I am will have suggestions for you. In the meantime, I have more questions than answers. Not trying to be picky, just trying to understand:

What maintenance other than the ignition tune up was done before this problem started? Was the ignition tune up done *just* before the trouble began? Has any service been done on the carburetor?

When verifying compression, did you use the 'thumb test' or gauge?

When pulling a plug wire, I'd expect rpm of a properly running engine to decrease, not for performance to improve, as I think you mentioned. Did you pull the wire for each plug?

You mention the fuel pump is clicking and pumping fuel. Have you checked fuel pressure?

Have you inspected the spark plugs?

By the time I submit these questions others may have solved your problem.

Best regards,

Jack.

[Catfish]

No problem, please be picky lol.

When verifying compression, did you use the 'thumb test' or gauge?
THUMB TEST
When pulling a plug wire, I'd expect rpm of a properly running engine to decrease, not for performance to improve, as I think you mentioned. Did you pull the wire for each plug?
I PULLED 2 AND 3, THINKING IF THE ENGINE RAN BETTER IT COULD BE EXHAUST BLOCKAGE.
You mention the fuel pump is clicking and pumping fuel. Have you checked fuel pressure?
OTHER THAN VERIFYING ITS SQUIRTING FUEL OUT OF THE FUEL PUMP, NO.

Have you inspected the spark plugs?
YES, SLIGHTLY BLACK SOOTY DRY

[Al Schober]

Sure sounds like fuel starvation.
Be advised than even a separate outboard style fuel tank needs a functioning fuel pump. It needs suction to get fuel out of the tank. And those outboard tanks are notorious for not feeding fuel when you need it. The O-rings in the connectors are known bad actors.
Try a stone simple gas tank - perhaps a coffee can with a hose nipple at the bottom. No connector to worry about, no siphon to get started. Just fuel coming out of a can. Connect direct to the carb (no fuel pump) and give it a try.
I'm a fan of a pressure gauge attached to the carb inlet. A glance at the gauge tells me I'm getting fuel or I'm not.

[Sam]

Hmm - quick answer, agree with fuel pressure comment, fuel pressure gauge should show exact pressure to carb. You need nominal 1 to 2psi steady state and your pump may not be maintaining. Also suspect coil internal shorting but that usually takes more than couple minutes- but maybe? My first go would have been faulty condenser based on similar experience but that's been changed out?? Possible float is sticking in carb - try giving it a gentle wack on bowel and see if you get improvement then quick clean with carb cleaner spray through drain plug. Finally your ignition switch may be faulty - by pass and try again. None of this is "final solution" - just quick temp fix finding the trouble area then take time for more permanent repair.

[Catfish]

Thanks Al. Will the engine run properly with just a gravity feed?

[jcwright]

Hello again.

Since no one else has responded yet, here are some thoughts:

Others on this forum have reported cases where the thumb test misses low compression. IMHO, a compression gauge is a good investment.

Suggest you pull each spark plug wire in turn to check for change (drop) in rpm.

A fuel pressure gauge is worth every penny, especially since your symptoms are consistent with fuel issues.

Unless I'm mistaken, your latest post does not mention what maintenance was done just prior to the problem. If you haven't already, check Moyer's video on carburetor maintenance:

https://youtu.be/kHuemGC_PHA

Good luck with you diagnostics.

J.

[roadnsky]

Thanks Al. Will the engine run properly with just a gravity feed?

I'm with Al. Sounds like you're "running out of fuel".
Yes, it'll run with a good gravity feed.

Also, double check that the black (-) wire running into the distributor is not getting pinched or shorting.

[JOHN COOKSON]

My A4 starts right up, idles great, accelerates good, but after running under power for 30 to 120 seconds starts sputtering and dies. It'll start right back up, but repeats the stall after a minute or two when under power.

You're running on one carburetor bowl full of fuel. When you crank the engine the fuel pump is operating and the carburetor is filling with gas and the engine starts. When the engine starts the cranking is finished and the key is in the on or run position the carburetor is not receiving any fuel for some reason and the engine quits.*
This is typical behavior when the OPSS is not working. What is the oil pressure and oil level? Is there gunk in the OPSS port that is keeping it from functioning properly?
When you try running off a auxiliary tank connect the fuel pump directly to the battery. This will bypass all the electricity routing to the fuel pump. Betcha this will be informative.
Best I can do for now. More later.
*With fuel pressure gauge you would be able to confirm or debunk this theory.

ex TRUE GRIT

[joe_db]

Thanks Al. Will the engine run properly with just a gravity feed?

Yes it will - sort of. The engine does not need much fuel, usually less than 1 GPH, and it hardly needs any pressure. 1 PSI is enough to make it run.
That said, when I had my fuel pump die in Saint Michael's, we connected the dinghy tank to the carb and tank sat in the cockpit about two feet higher than the engine. The engine would run for a while, but in that assembly of connections and the squeeze bulb there must have been a tiny air leak, usually around the 15 minute mark it would quit.
My wife was getting tired of me telling her "We are losing power - squeeze it until firm!" by the time we got home So.....gravity feed works, outboard tanks are iffy.

[edwardc]

If you have a Facet fuel pump, it sure sounds like the notorious "stuck ball" problem, resulting in fuel starvation.

The test and temp fix is simple. Remove the bayonet bottom of the fuel pump. This will expose the bottom of the check valve ball. With a fingertip, press gently on the ball. It should move smoothly against its spring.

if it doesn't move, apply more pressure. It should suddenly snap free with a perceptible "click" and operate smoothly afterwards. Close up and retest.

Unfortunately, this is only a temporary fix, as I have found that once the ball starts sticking, it will do so again. Only permanent fix is a new pump.

Anyway, try it. Its easy and only requires a few minutes. Let us know how you do.

[Catfish]

Still no luck. I bypassed the OPSS and fuel pump, by hooking up a new fuel tank, primer bulb/hose, and a cheap clear filter to help me see, and have it gravity feeding the carb. Getting the same result. I took the carb apart again this morning and cleaned it. The float and valve seem to be working fine. I ran a wire from the battery directly to the coil and that didn't help either. The plugs look good, dry with a little black around the outside. I'm running out of things to check. Fuel pressure gauge on order.

The engine will idle all day long. It goes into gear and comes up in RPM fine, but after about 30 to 45 seconds of running in forward, I can hear it start to lose power and then shut off.

[Peter]

a fuel pressure gauge would be an excellent diagnostic tool for this issue.

If you watch it will running in gear and the fuel pressure remains solid, not a fuel delivery problem. If the pressure falters, a fuel delivery problem.

Having solid information about this will help you to quickly narrow down the issue.

These gauges are cheap and easy to install. If you plan on leaving it in permanently, make sure you get a metal one for fire safety purposes.

If you just plan on using it temporarily, you can get cheap plastic ones at an auto parts store.

Hope that helps,

Peter

[JOHN COOKSON]

The engine will idle all day long. It goes into gear and comes up in RPM fine, but after about 30 to 45 seconds of running in forward, I can hear it start to lose power and then shut off.

Main jet problem. Or the advance.
The main jet can be tricky. There are a lot of threads to install the main jet. if they get bunged up the main jet will not seat correctly and as a result not work correctly.
This exact scenario happened to me.
Took me awhile to figure it out.

Aren't boats fun? Sort of like personal relations. When they're good they're great. When they are bad they're REALLY bad.

ex TRUE GRIT

Edit: As I recall there needs to be a washer on the main jet passage plug. Did you leave it out by any chance?

[Catfish]

Hmmmm. I can't help but think it's fuel system related either, but I'm trying to keep an open mind and be a methodical troubleshooter (but I'm at the point where I'm just throwing parts at it LOL). I know there was a small washer on the main jet, but the plug does not have one. I'll look into that today and report back.
I know I have an old carb laying around that came with the boat when I bought it. Going to get it out of storage and look at the possibility of rebuilding it as well. My girlfriend and I are moving aboard our Catalina 30 and need to get her running right for a short jaunt to our new marina home.