Starving for fuel

[Boorskis]

I have a 1978 90HP, 6 cylinder Mercury Outboard that has a fuel problem. It seems to run OK cold and when not under load, but when warmed up at full throttle, it will run out of gas and actually shut down if you do not pull up to idle. If someone slowly pumps the inline primer ball, the engine picks back up and will at least get you back to the dock. I have rebuilt the fuel pump recently and don't think that is the problem. Could the line from the top cylinder to the fuel pump be bad that provides the pumping pressure/vacuum? Might I be losing compression in that top cylinder when the engine warms up? Is it possible to replace the mechanical pump with an electric fuel pump on this engine?

 

[hkeiner]

Re: Starving for fuel

I suggest performing the below described tests to troubleshoot the problem. Systematic troubleshooting is often quicker and less frustrating than replacing/repairing parts until the problem is solved. Also, I wouild not suggest replacing the mechanical fuel pump with an an electric fuel pump. There are some dangers to using an electric fuel pump, which keeps running when the motor dies and/or a fuel hose breaks.

Another quick test for fuel starvation is to hook up a portable tank to the motor to see if the problem goes away. If it does, further troubleshoot the fuel line and fittings upstream of the fuel pump. If it does not, further troubleshoot the fuel pump and carbs. Just my thoughts...

 

[Chris1956]

Re: Starving for fuel

I would think that motor has two pulse/vacuum lines going to the fuel pump. You might check them for cracks. They should have hose clamps sealing the ends.

Also check the oring seal in the plastic strainer cover to make sure there are no leaks. Finally if when using the remote tank, the motor does not have the problem, it could be a bad antisiphon valve in the main fuel tank, or a bad fuel primer bulb.

 

[FireCapt]

Re: Starving for fuel

I had a very similar problem as yours about two months ago. The engine ('92 merc 150) would start and run fine until I pulled away from the dock and got her on plane. The engine would then shut down as if I turned the key off. I could restart it and run slightly rough at idle but I would have to push the key in to give it a shot of fuel to every once in a while to keep it running. If I advanced the throttle it would die.

I realized that I didn't put stabilizer in the fuel before winter and immediately I was concerned of a fuel issue. I siphoned the fuel out of the fuel tank and drained the old fuel out of the bottom of the carbs. I refilled the tank with fresh fuel with a dose of stabil and went out to try her out. She ran like a champ and has been great ever since then.

Some marine mechanic friends indicated that the ethanol has probably separated from the gas and my motor was probably trying (quite unsucessfully) to burn a ethanol/water mixture. I decided that I will use fuel stabilizer with every tank of fuel from now on.

 

[jerryj326]

Re: Starving for fuel

I have a 40hp 2 cyl. mercury. I can start it and run it at slow speed, but when i give it the trottle, it goes for about 2 minutes, and the stops.
I replaced the fuel pump, and the impellar. Thought motor was overheating and stops? But hat did not solve the problem?? Did the cleanning of the gas tank solve your problem???