Need advice. Engine cutting out

[dschild]

First sea trial. Boat ran for a couple hours. Cruising is about 37 mph. Everything was fine for the first hour. I tried not to keep it at WOT for most of the time.

After an hour we started noticing it struggling when we throttled down. Then the motor died.
Started up again and as long as we maintained cruising speed it was healthy so we headed back to the dock. About a mile away I had to throttle down and it quit again.
The motor would start up, but as soon as I engaged the gear (forward or reverse) it died.
I tried letting it idle and it would die after a minute. We repeated this three times. Then left it. Had to paddle back to the dock.
Got home and hooked it up to the hose. This is about 45 mins later. The motor started up and ran idle for fifteen mins. No problem.

Info
1976 Mercruiser 165 HP
MC1 Leg.

I replaced plugs and wires a week ago.
I put 5 oz of seafoam in the crankcase, ran it on a hose, and then changed oil a week ago.
Replaced water pump yesterday.

 

[QBhoy]

Is this the 3.7 4 cylinder? If so, did you do both water pumps ?

 

[Scott Danforth]

470 4 cylinder or 230 cubic inc 6 cylinder?

First thought, look at the fuel system

 

[kenny nunez]

The problem you are describing points to the rotor in the distributor. They get so hot that the spark goes right through it. Just like you described it restarted after cooling down. Take your rotor to a Mercruiser dealer and compare the length of the blade. If there is no Mercruiser dealer go to NAPA and compare what they have, the main thing is the blade needs to be slightly longer than the one you have. Another thing to think about is to convert the ignition to a Petronics electronic kit.
The electronic ignition does not generate as much heat in the distributor and does not effect the rotor as much.
Always keep a spare rotor should the same thing happen again, if it does swap the rotor to be sure that is the cause.
Is the engine cover ventilated enough ?

 

[andrewterri]

As scott danforth said look at the fuel system. First thought that came to mind was fuel take pressure from a stuck check valve. Easiest way i know of to check it is when you have ran the boat and it is acting up unscrew the fuel tank cap and see if there is a lot of pressure. Also, when was the carb last clean? Not coming off power could be a stuck float. Did the engine seem flooded to you? I am sure the experts will continue to chime in but those are my thoughts.

 

[dschild]

Thanks for the advice, all. The fuel ventilation is something I could / should have easily checked while I was out there.

The motor is the inline 6. The GM 250 from what I understand.

I think im going to look into changing fuel filter and thermostat and maybe fuel pump myself. Those are things I’m capable of doing. But I’ll take it to a mechanic for a carb rebuild.

When I changed the plugs and wires the shop recommended I replace the distributor. I didn’t think I needed to then. But maybe I’ll revisit that too.

I was was surprised that after 1.5 - 2 hrs half the tank of gas was gone. Is this pointing to it possibly running too rich?

 

[andrewterri]

The fuel usage would depend on you tank size, rmp, and prop you are currently running. If you were running at cruising speed for two hours straight that sounds about right to me. You can change the fuel pump if you want but you will learn, if you don't already know, that throwing parts at an unknown problem will only get expensive and make you frustrated. It is much better to diagnose through process of elimination. The guys/gals on this forum are great and will help walk you through what needs to be done to figure it out.

Do you know why you were told to change the distributor? If that was the problem I would think the symptoms would be much more consistent. To run several hours which would include idling at some point just fine than all of a sudden start having problems is why im with Dan thinking fuel system.

In regards to the carburetor, it is very simple to clean and rebuild. I bet a shop will charge you around 200 while you can get a rebuild kit and a can of b-12 for less than 50. There are multiple write-ups on here and the internet. I would guess you have a mercarb 2 barrel (not sure the years they used rodchester) and there are numerous step by step videos.

The check valve is on the hose running from the tank to the fuel pump. where the hose attaches to the tank is about a 1-2 inch piece of metal that looks like a hose barb. That is the check valve and screws onto the tank fitting.

Have you checked your plugs yet? That will help give you an idea if you are running rich.

 

[dschild]

Carbs always intimidated me. But if I’m going to learn to maintain this boat then I guess I best learn. So ya, I’ll check out the write ups. I did change the plug and wires. The guy who sold me the parts suggested I change the distributor too as a common practice. Having never heard of that I declined.

I’ll check the valve. That sounds simple. What am I looking for on the plugs that would indicate running rich?

 

[dschild]

Quick google search showed me what to look for on the plugs. I’d say yes, running rich.

 

[dschild]

FYI compression tested near 150 for all six cylinders.

 

[andrewterri]

They might have been talking about cap and rotor which is standard practice during a tune up but not the entire distributor. sounds like you found what you needed to know about the plugs. if they are wet with a lot of carbon you are running rich. i would replace your inline fuel filter and clean/rebuild that carb. it is very easy just don't let it intimate you. if you run into any problems come to the forum and create a post with what the hang-up is. i would buy all new needle and seats for the carb, some kits come with them and some don't. Not all people replace them but i always do. the seats just unscrew with a flathead its very easy. if you are on a budget you can just clean them with carb cleaner, no wire brush. i think this is where your problem is. other members will throw out other ideas too.

 

[Scott Danforth]

Thanks for the advice, all. The fuel ventilation is something I could / should have easily checked while I was out there.

The motor is the inline 6. The GM 250 from what I understand.

I think im going to look into changing fuel filter and thermostat and maybe fuel pump myself. Those are things I’m capable of doing. But I’ll take it to a mechanic for a carb rebuild.

When I changed the plugs and wires the shop recommended I replace the distributor. I didn’t think I needed to then. But maybe I’ll revisit that too.

I was was surprised that after 1.5 - 2 hrs half the tank of gas was gone. Is this pointing to it possibly running too rich?

its probably not your fuel pump unless there is fuel in the clear tell-tale hose

no need to replace the distributor. cap/rotor/wires - yes. points - yes, that is replace them once every 20 years, however you do need to file, gap, and adjust them every spring. however, no need to replace the dizzy. and if the bushings in the dizzy are sloppy, napa has them for under $5

 

[andrewterri]

Scott. so your saying i didn't need to adjust my dwell angle every spring while waiting for the water to warm up :laugh:

 

[andrewterri]

dschild, it sounds like you have a healthy engine other than the carb. Find a good write up or video, order the parts, take your time along with plenty of pictures and you will have a great running boat.

 

[Scott Danforth]

Scott. so your saying i didn't need to adjust my dwell angle every spring while waiting for the water to warm up :laugh:

no, you do need to file your points, verify the gap and adjust dwell angle every spring. that is just the price to pay for points type ignition.

 

[dschild]

Thanks, all. Great community!

 

[dschild]

Ok here’s the latest. Timing was 10° off. Idle was sticking when hot. Floats needed adjustment. Cleaned the points. Took the boat out today. Cruised for about 45 minutes, everything sounded good, had to slow down for some traffic, and the engine cut out. Remembering what happened last time, I waited about 20 or 30 minutes, and started the engine back up. Engine started up, I waited for it to warm up a little bit, and started making my way back. The engine lasted almost until we got back to our launch. It started acting like we were almost out of gas, (had over half a tank). Meaning it was gradually slowing down and sputtering. Until it finally just quit. Again I let it cool off about 20 or 30 minutes And restarted and made my way back to the launch. Fuel line was cold to the touch. Motor itself seemed reasonably cool. Meaning I could put my hand on it. Felt warm but not hot. Temperature gauge on the console was half way up.


Successfully having returned to the launch I was able to drive up onto my trailer and make it home. A successful day in my opinion. But still have this issue.
My mechanic suggested that the coil may be soaking heat from the motor. Going to look to replace that. Seems I can get one replaced for about $50. I’ll give that a try.

 

[dschild]

Ok here’s the latest. Timing was 10° off. Idle was sticking when hot. Floats needed adjustment. Cleaned the points. Took the boat out today. Cruised for about 45 minutes, everything sounded good, had to slow down for some traffic, and the engine cut out. Remembering what happened last time, I waited about 20 or 30 minutes, and started the engine back up. Engine started up, I waited for it to warm up a little bit, and started making my way back. The engine lasted almost until we got back to our launch. It started acting like we were almost out of gas, (had over half a tank). Meaning it was gradually slowing down and sputtering. Until it finally just quit. Again I let it cool off about 20 or 30 minutes And restarted and made my way back to the launch. Fuel line was cold to the touch. Motor itself seemed reasonably cool. Meaning I could put my hand on it. Felt warm but not hot. Temperature gauge on the console was half way up.


Successfully having returned to the launch I was able to drive up onto my trailer and make it home. A successful day in my opinion. But still have this issue.


My mechanic suggested that the coil may be soaking heat from the motor. Going to look to replace that. Seems I can get one replaced for about $50. I’ll give that a try.

 

[dschild]

I’m not sure why that doubled up. I can’t delete one of them. Sorry for the duplicate

 

[andrewterri]

"Meaning it was gradually slowing down and sputtering"

Your getting to much fuel or not enough. You know what to look for on the plugs. Did you unscrew that gas cap when you were letting it cool off to see if there was excessive pressure? Never heard of a coil absorbing heat and acting up like that but guess its possible. So basically after the timing adjustment and other stuff things didn't get better or change?