79 165hp stalls under load

[Menace2Authority]

I've made a couple other posts on my "issues" however as symptoms have become more clear I figured I'd start another post.

1979 Mercruiser 165hp in line 6 cyl.

Initially, the boat seemed to be stalling and not re-starting once it got warm. So this morning I bought a new coil for it. Fired it up and let it idle at the dock for about 20 min. Rev'd it up to about 3000 rpm with the engine good and warm and it didn't stall. So I assumed I may have fixed the problem. Later in the day I decided to test drive the boat around in front of the dock. Putted around a bit very slowly with no problems. Gave the boat about 3/4 throttle and about 2 seconds after it planed out it stalled. Again.... it wouldn't start. It would fire and briefly sputter, but would not stay running. Within 5 minutes of it stalling I was back at the dock thanks to a nice fellow boater who towed me. As soon as I tied off, I gave the boat some throttle, turned the key and it fired right up and idled nicely for 15 min or so. At that point I again gave it throttle in "neutral" and still it ran fine. I shut the motor off and with it hot I did a compression test and compression was 120 across the board (give or take a couple pounds).
When the boat stalls it feels as though it's running out of gas with a few caughs/chugs before dying.

So....
-Engine stalling under a load. Running fine in neutral
-Starts real good
-Good compression when warm
-New Coil
-Plugs all look good
-Full tank of new gas and the "pump ball" on the fuel line is hard so there's good fuel flow at least to that point.
-Boat won't run long enough in gear to over heat it and in neutral has only gotten to about 145 degrees.

Any ideas? I'm stumped here and even the couple mechanic friends I have are having a hard time offering advice.

Thanks,
Rob

 

[JustJason]

Re: 79 165hp stalls under load

Start with the boat side fuel system test as written in the Adults only section.

Verify your timeing, firing order, and make sure the point dwell is set correctly, plugs look good and plug wires that don't leak.

Then after all that... It sounds like a boogered up carb, but you really should verify everything else first.

PS- You don't need a fuel primer bulb in an IO. Get rid of it and replace the entire line with 3/8ths A1 CG approved fuel line, and make sure you double clamp the barbs.

 

[Menace2Authority]

Re: 79 165hp stalls under load

Thanks for the suggestions. I will check the fuel filter tomorrow and probably replace the fuel line as my next step. A collapsed fuel line definately fits the symptoms. Especially since after 10 min or so the boat will fire back up and run great again until large fuel consumption is required. Will there be a filter or screen inside the tank that I should also be checking? It's a Mirax fuel tank.

Thanks
Rob

 

[kilowatts]

Re: 79 165hp stalls under load

Hi Guys:

I have the same rig as you. Yesterday I had the same symptoms when on the water. I had installed the small fuel filter in the Rochester carb backwards and was starving the engine when under load. I hope yours is as simple as mine was.

kilowatts

 

[Menace2Authority]

Re: 79 165hp stalls under load

I tHought about the carb fuel filter but when I removed the nut there was none. Only a spring in there.

 

[Menace2Authority]

Update!

Update!

Pulled in-line fuel filter off and its quite hard to blow through so I put a new one on. Scary part is this... With the gas that I poured out of the fuel filter and what ran out from the fuel pump to the carb (which wasn't much) I got probably about 1/8th of a cup of water in that fuel. Most likely being the cause of my problems. I'm assuming th?t there will also be water in the carb? Or would the fuel pump have blocked the water from getting through? The boat had 2 primer bulbs in-line BEFORE the filter. One bulb had a pin hole in it and seeings they were laying beside the bilge on the bottom of the boat I'm sure this is where the water was coming from.
So finam question is... Would water have made it past the filter to the carb?

Thanks again for all the help.
Rob

 

[kilowatts]

Re: 79 165hp stalls under load

Hi Rob:

In my opinion, yes the water would get through.

To recap: The pick up in the tank sometimes has a filter screen on it which can get clogged, so that should be checked if possible. The fuel line from the tank should be the correct grade and size, no bulb. This line should go to a spin on type water separator filter and then to the pump. The fuel pump should have a new filter in it. Correct line from the pump to the carb, no inline filter and then the correct filter in the carb. If these items are all correct and the gas is clean I think you could say that the fuel delivery system is in good shape.

Good luck.

kilowatts

 

[Menace2Authority]

Re: 79 165hp stalls under load

Hi Rob:

In my opinion, yes the water would get through.

To recap: The pick up in the tank sometimes has a filter screen on it which can get clogged, so that should be checked if possible. The fuel line from the tank should be the correct grade and size, no bulb. This line should go to a spin on type water separator filter and then to the pump. The fuel pump should have a new filter in it. Correct line from the pump to the carb, no inline filter and then the correct filter in the carb. If these items are all correct and the gas is clean I think you could say that the fuel delivery system is in good shape.

Good luck.

kilowatts

Well my fuel delivery system is a train wreck then. No water separator, no new fuel filter in the pump, and no filter whatsoever in th carb. Looks like a trip to the parts store this week.

Rob

 

[Menace2Authority]

Update ii

Update ii

Boat seems to run just fine now. I am still however going to take all the above advice and points listed above and make a trip to the parts shop this week. Thanks to all for your time. Hopefully I'll be able to contribute to you all some day if you're ever stuck.
Rob

P.S. 38 mph on gps