'77 Mercury, 115hp Outboard. Dies...

Hi, i just bought me a '77 Charger with a 115hp Mercury Outboard engine.
The engine runs like a champ while i have it sitting on my driveway, connected to the waterhose.
When i launched it yesterday, it only ran for about a minute in the water , then died on me.
I fired it up, it ran another minute then died..I tried this for a few times with the same result. Couldn't figure anything out.
Took it home, connected it to the hose, and it ran for 30 minutes til i shut it off!

The seller told me it has a new waterpump.

I'm a carguy, this is my first boat. I'd highly appreciate any tips i could get.

Thanks / Hank

Re: '77 Mercury, 115hp Outboard. Dies...

Hank, when it was running in the water was that at idle or at speed? It definitely sounds like a fuel problem, on muff with no prop in the water there is virtually no load on the engine. Fuel goes a long way with no load. If you have a poor fuel delivery system you wont notice it. On the water it will show up right away. You need to develop 4 to 5 psi fuel pressure for the inline 6 mercs to run at full throttle. Likely culprit is the fuel pump itself, there is a very inexpensive kit to rebuild it. Secondly, there are filters in the top of the fuel bowl on each carb. They are located behind the fuel line, you will not see them if you do not disconnect the hose at the carb. remove these filters and do not re install them, insead, put a good quality marine fuel filter in the main fuel line. Since you now have the carb fuel bowl tops off, check to make sure the needles and seats are ok and that the float level is set correctly. Obviously, check for crud in the bottom of the fuel bowls as well. If they are dirty or corroded they must be cleaned up and carb kits put in. Carb kits are also available quite cheaply as well. Keep posting and we will get you running.

Re: '77 Mercury, 115hp Outboard. Dies...

I agree with Dave of course, but would also ask what rpm that it idles at and what speed you were running when it died? If this is at idle, it may just be an idle rpm adjustment required to kick it up a notch and/or an idle mixture adjustment, or both... running in the water will reduce your idle rpm significantly in comparison to running in the driveway due to the water exhaust back pressure Dave mentioned.

Re: '77 Mercury, 115hp Outboard. Dies...

Hey guys, thanks alot for your advice. Well, i was running it at idle, so not very high rpm:s.
I did feel that the idle was too low though, and i wanna try to kick it up a little.
I had someone give me the advice to install an electric fuelpump and an pressure switch between the marine fuelfilter and the engine?!

Also, the fuelhose is a rubberline all the way from the tank and back. I do know from working on cars that old rubber hoses actually can work as a "valve' and prevent the fuel from coming thru, so i'll replace all hoses tomorrow.

I will take the top of the carbs and clean the bowls out too...

Re: '77 Mercury, 115hp Outboard. Dies...

Hank, That '77 should have backdrag carbs. They have a stainless screen under the brass fitings that screw into the carb covers. They should be completely clean.

Rebuild the original fuel pump. Do not install an electric pump, they are quite dangerous, since you do not have a good way to turn the fuel pump off if the motor stalls or doesn't start. it is a fire hazard.