Runs great, but stalls out under power

[roadnsky]

Note this caution regarding the washer INSIDE the Main Jet...

"CAUTION: Both the fixed jet and the 1/2" hex-headed plug of the needle assembly have hard washers to seal them after installation. Use care in removing the original fixed jet so as to not lose the original washer. If the original washer remains in the carburetor instead of coming out with the jet, it's usually preferable to leave it in place and save the new washer for a spare. Do not end up using both small washers behind the fixed jet."
(From the instructions for installation of adjustable main jet)

Worth checking if that washer is in place.

I know there was a small washer on the main jet, but the plug does not have one.

I think the washer you are referring to is this one? (see pic).
The MAIN PASSAGE PLUG.

[Catfish]

Yes, that's the one. I pulled an older 4 bolt zenith carb out of the drawer and cleaned it all up this morning. Engine fired right up and idled for a few minutes. I put it into gear while tied to the dock and brought the rpm's up slightly. After about a minute of running the engine did the exact same thing. It sounded overcome, the RPM's dropped and it died. It will immediately restart, weather in forward gear or not.

I have a new fuel can, new primer bulb and hose, gravity feeding from the roof of the cabin. I can see the clear fuel filter completely full while the engine is running and when it begins to die. While it seems fuel supply related, at this point I can't help but think something is getting warm and creating a disconnect, or something mechanically is seizing? Not sure what to troubleshoot next.

[roadnsky]

Ok, I know you said you checked it, but now we're gonna need to methodically go thru until we find the issue...
which, we WILL.

Can you double check or triple check you have the firing order correct?
(I know, just humor us here)
See the attached DOC and check 'em.

Another one...
Did you check the Stuffing Box?
Last time adjusted?
What is it's condition?

[jcwright]

There are at least two reports on the forum with vaguely similar symptoms -- idles ok but dies when powered up -- that were reported not to be fuel related. If I recall correctly, one of them was a packing gland that did not seem too tight at first, but then seized up repeatedly under power. And another that turned out to be due to 0 valve clearance.

I'm not suggesting that either of these is likely to be the cause of your symptoms, but then neither did the people who went down these rabbit holes. The seizing packing gland would be easy to check, as it would be warm or hot after shut down. I don't know of a quick way to check the valve clearance, as you'd need to remove the valve cover, so if we're me I'd wait on that for others to offer better ideas.

[ndutton]

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.

So what is different when the engine is in gear?

1. Prop shaft is turning - RoadnSky is all over this. Loosen the stuffing box so it drips profusely and do another run test.
2. Fuel consumption is much greater - when it quits and without restarting I'd like to know the fuel level in the carburetor bowl at the instant it quits.
3. Engine temp increases - although 30 - 45 seconds would not produce a significant temperature rise so let's set this one aside for now.

[Catfish]

I checked the firing order and had my girlfriend check as well. Just in case I've lost my mind (almost there). I've checked the stuffing box after running for a few minutes and it is cool to the touch and the shaft spins freely when popped into neutral. The stuffing box was repacked last year and had some miles on it before this problem manifested itself. I fired the engine up and started checking a few things with my multimeter.
I was using a test light and when laid across the contacts of the coil while running it was lighting up. However, I put the multimeter across it and am only getting 3 to 4 volts. The impedance when shut off is only registering .01 ohms. My input voltage is reading 12v to the coil. Could this be a bad coil? Should I be getting 12v when I test across the coil while running?

[JOHN COOKSON]

the shaft spins freely when popped into neutral. The stuffing box was repacked last year and had some miles on it before this

There could be something wrapped around the prop. For me it was a palm frond. The shaft turned easily by hand from inside the boat. When the engine was put in gear the centrifugal force of the prop rotating flung the frond outward stoping the engine. The diver who cleared the frond told me all this.

ex TRUE GRIT

[Catfish]

Thanks John, I had my diver check that when I started troubleshooting and it's clear and clean. It appears I have a bad coil. Going to try and find one today (observed holiday). It has no resistance when I test it. Wouldn't think that's the issue with the symptoms I'm getting, but stranger things have happened. Especially with this engine.

[roadnsky]

I was using a test light and when laid across the contacts of the coil while running it was lighting up. However, I put the multimeter across it and am only getting 3 to 4 volts. The impedance when shut off is only registering .01 ohms. My input voltage is reading 12v to the coil. Could this be a bad coil? Should I be getting 12v when I test across the coil while running?

Please note that the coil's INPUT VOLTAGE should be tested between coil + and a solid ground (block). Not the coil's (-) terminal.
The small coil (-) post is not a "ground" even though one would think so with that label.

[Catfish]

Still trying to get this old girl staying running for more than a couple minutes. I replaced the fuel pump today and rigged myself up a gravity fuel feed. Just a gas can with the top cut off and a nipple installed in the bottom and no fuel filter. Still getting the exact same result. Engine fires right up. Idles well all day long. Goes into gear at any rpm and the engine is responsive to throttle. but after running against the dock lines for between a minute to three minutes it dies. Same issue with either carburetor I've tried. Ignition seems good, fuel and delivery seem good. Drivetrain????????

[JOHN COOKSON]

Is the choke adjusted correctly? When the engine starts to die does closing the choke help it to run longer?

ex TRUR GRIT

[ndutton]

Quoting myself from 4 days ago:

when it quits and without restarting I'd like to know the fuel level in the carburetor bowl at the instant it quits.

[Catfish]

John - I have the choke cable disconnected so it is completely open. I've visually verified as well.

ndutton - I've tried to do this but by the time I get the fuel shut off and the carb unbolted it's full. Don't know if it's from the time it takes me to do that, or if it's staying full. I've tried 2 different carbs, and today a straight gravity feed fuel system with a new fuel pump and hoses. Getting the same result.

[roadnsky]

...by the time I get the fuel shut off and the carb unbolted it's full.

Next time run it WITHOUT the Flame Arrestor on the carb.
That will allow you to look into the BOWL or Throat.
If you can't see clearly, stick your phone in there and take a bunch of shots.
We're looking to see if fuel is pooling in there.
(Neil, speak up if this isn't where you were going)

[ndutton]

(Neil, speak up if this isn't where you were going)

No need. All I'm trying to do is garner as much pertinent information as possible rather than jumping to conclusions or guessing.