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  #1   IP: 35.143.211.72
Old 07-01-2021, 08:02 PM
Catfish Catfish is offline
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Runs great, but stalls out under power

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?
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Old 07-01-2021, 09:14 PM
jcwright jcwright is offline
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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.
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Old 07-01-2021, 09:30 PM
Catfish Catfish is offline
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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
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Old 07-01-2021, 09:45 PM
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Al Schober Al Schober is offline
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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.
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  #5   IP: 108.12.235.34
Old 07-01-2021, 10:06 PM
jcwright jcwright is offline
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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.
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Old 07-09-2021, 09:08 PM
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Quote:
Originally Posted by Catfish View Post
I PULLED 2 AND 3, THINKING IF THE ENGINE RAN BETTER IT COULD BE EXHAUST BLOCKAGE.
Exhaust... Bingo!
So glad you've found this. (Feels good 'eh?)

I guess some of us wrote off the exhaust blockage too easily. (me)
Sorry. It seems so obvious now.

Cat-
This is one reason you got so many questions even tho you had (in theory) crossed off that issue on your checklist.
It is the hardest part of contributing on this forum...
Troubleshooting remotely without the benefit of the senses of seeing, smelling and touching.
AND... the keystone of this forum...
Being reluctant to offend or "flame" someone in expressing an opinion.

So... celebrate your troubleshooting and DYI skills! Congrats!
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Old 07-10-2021, 08:00 AM
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Thank you Jerry. It does feels great. I was at wits end and had started researching electric engine conversions lol. Thank you EVERYONE for your contributions to this thread. I've always been a cheerleader for the A4. I hope I can give back to this forum as much as I've taken. If any of you are ever in the gulf beaches area of St Petersburg Florida please accept my invite for coffee or a cocktail.
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Old 07-10-2021, 04:38 PM
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not the first time on this forum: air, fuel, spark.... and an open exhaust!
Well done!
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Old 07-01-2021, 09:49 PM
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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.
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Old 07-01-2021, 09:59 PM
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Thanks Al. Will the engine run properly with just a gravity feed?
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Old 07-01-2021, 11:06 PM
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Quote:
Originally Posted by Catfish View Post
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.
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Old 07-02-2021, 07:43 AM
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Quote:
Originally Posted by Catfish View Post
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.
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Old 07-02-2021, 12:19 PM
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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.
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Old 07-02-2021, 12:38 AM
JOHN COOKSON JOHN COOKSON is offline
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Quote:
Originally Posted by Catfish View Post
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
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