motor trouble

[oldmerc18]

Hello,
I'm new to this site and a friend thought someone could help me. I was coming in from fishing a couple nights ago with my 1976 85hp 2 cycle merc and the engine rpm slowed very fast and the motor stopped. By the sound of it I thought i blew it up. After looking it over I tried to restart and it started with a slight miss but cleared up. I continued my trip to shore getting to my normal top speed and it died again.(bad sound more than a miss or running out of fuel). I did this a third time and it quit again.
Looking it over in the garage i found the rectifier had burnt leads and have one ordered. I think the rectifier only converts alternator ac to dc to charge the battery. The battery is charged everytime my boat is sitting so that could of been a old problem. The battery was good when restarting the boat.
Anybody ever have a similar problem that could tell me what

[Burr]

Check your fuel tank vent to make sure you are venting your tank effectively. Did you notice if the primer bulb was flat from a suction effect on the gas line?

The other thing that comes to mind is when is the last time the fuel pump has been rebuilt? These older motors had a diaphram fuel pump, that often worked so well that nobody ever thought about putting in a rebuild kit. It's a good idea to rebuild the fuel pump with a kit (they are not expensive) if you have not done it recently. It would not surprise me to hear the pump has never been taken apart (paint is not off the screws) - and after 27 years it might be time.

I had that motor years ago, if I did not use the motor for a month or so, I would have a gas leak on the motor from a diaphram that would dry out. I would just take off the cover, re-install it, and it would seal up. But that problem was most often one that would not allow me to start the motor. Once I had that cover sealed up, it would work until it sat for a month again.

[mudpuppy]

If I have a motor stall while running the first thing I do is check the fuel bulb. Is it firm.Is it soft. Or maybe collapsed. Have you changed the fuel filter lately? Is the gas fresh? The next thing I usually do is pull each plug individually and inspect them. Are they all the same color? Oily? It's hard to tell from your description. Sounds like fuel delivery problem. Does your boat have a remote tank or a built in tank? If it's built in try hooking it up to a smaller remote tank with fresh fuel and see if the problem persists.

[oldmerc18]

Thanks for your replies Mudpuppy and Burr. I went through all the fuel system and found no trouble. Went to next step and checked compression. 3 cylinders had 150 psi and one had 25 psi. I don't know how it restarted and got back to speed, (for about 30 seconds) but I think i need a new motor.