1980 Mercury 115 Looses Power after running for a while

[shekinah5678]

Hello I have a 1980 mercury 115 that I have a problem with. First off it is fairly hard to start after sitting for a day or so. Usually takes a small burst of starting fluid then it kicks off and goes. No problems getting started after that. The big problem is when I get it out on the lake. First of all, I have to lightly ease it into gear or it dies. Once its going it goes great planes out fast and sounds strong. After a few minutes of running at mid to full throttle it just starts to loose power and eventually dies. I can usually get it restarted but have to ease it back to dock. Then it sits and runs fine while at idle. At the lake I checked to see that the fuel line was not kinked and that the fuel filter was not clogged. Both were fine. I haven't done anything else yet thought Id see if anyone could give me a starting point. Should I have the carbs rebuilt or is it somthing other than fuel related. The boat has sit for a over a year so I know doing the carbs wouldn't be a bad idea. Any ideas would help. Thanks

 

[Chris1956]

Re: 1980 Mercury 115 Looses Power after running for a while

First of all, how long does it run at WOT, before it starts to die? If you pump the fuel bulb, does it get better? If so, you need to rebuild the fuel pump. It also sounds like the carb idle jets are not set correctly or are dirty, which is why you motor dies in gear at idle.

You really want to skip the starting fluid. it is bad for the two-cycle motors. Choke the daylights out of it to start it, or spray some premix into the carbs to start it.

You might like to richen up the carbs idle mixture (1/8 turn CCW) starting from top carb, then mid carb, then bottom carb, testing acceleration each time.

 

[shekinah5678]

Re: 1980 Mercury 115 Looses Power after running for a while

The motor runs for several minutes, probably about ten with no problems. I will try to pump the bulb and see if that helps and also try to adjust the idle mixture. I'll throw the starting fluid out thanks for that tip. I'll get back to you after I try.

Thanks again
Brad

 

[studlymandingo]

Re: 1980 Mercury 115 Looses Power after running for a while

Ditto on the starting fluid. You have to choke the living crap out of these motors when cold. It does sound like a fuel pump and squeezing the bulb is the way to find out. It could also be a clogged tank vent, it pulls fuel until the suction in the system is too great for the fuel pump to overcome. If the bulb squeezing brings no relief, check the tank vent.

 

[Texasmark]

Re: 1980 Mercury 115 Looses Power after running for a while

I had an '89 115 and had similar problems which I corrected by cleaning up the routing of my fuel line. It was really thirsty to start and at high rpm's I could run it out of gas; both of which I corrected temporarily by squeezing the bulb, which is what put me onto a fuel deficiency problem.

You may need a new diaphragm in your fuel pump, but you might clean up your fuel line from the tank to the engine first. Make it as short as possible and eliminate any unnecessary s curves or kinks. On starting, squeeze till firm, activate your "fuel enrichment" switch, crank for 10-15 seconds, and resqueeze the bulb. Should lite off much faster.......it's a long way up that engine to pump fuel......needs all the help it can get.

Mark