1985 50 HP Mercury losing power

[RickyRegs]

A 1985 Mercury 50 HP 4 cyl is losing power; it starts on first crank, idles fine, and get up to WOT like normal. After a few minutes, it loses power. This starts my "skipping" or have "power surges".

I just rebuilt the carbs and had a couple issues with flooding that i have now fixed as well to get me up to WOT.
It is possible the idle screw is not set properly, could this cause the issue? If yes, what would be the best method of setting this properly?

It is also on a gas tank that has only given me problems and needs to get back to an "ethanol friendly" metal tank with new "ethanol friendly" gas lines.

 

[194269]

Re: 1985 50 HP Mercury losing power

I think you have already answered your question. First if it idles fine leave the idle needles set where are. second replace the tank (you did say it was a problem) change all fuel lines, totally clean your fuel pump and carbs. Third, why do you want to use "Ethanol base fuel" I run ethanol free premium fuel in my outboards. Its a much better fuel when used in the older outboards. Just my .03 worth.

 

[RickyRegs]

Re: 1985 50 HP Mercury losing power

As i assumed, thanks.
I don't necessarily want to run ethanol - but, sometimes it is just more easily available than running down to one of the local marinas to get fuel. I typically keep about 20 gallons of non-ethanol fuel in my garage but sometimes it isn't feasible (or possible) to get ethanol-free gasoline - especially if i am out of town.

 

[MacDaddy21]

Re: 1985 50 HP Mercury losing power

Ricky, I can give you the process to adjust the idle mixture on your carbs if you still want it.

 

[RickyRegs]

Re: 1985 50 HP Mercury losing power

it wouldn't hurt to be sure i suppose.
i did what the manual said - but, as i have heard sometimes it is best to just close the manual and get it done.

 

[MacDaddy21]

Re: 1985 50 HP Mercury losing power

Well if you followed the process in the manual, you should be fine.

Turn the screw all the way clockwise until lightly seated. Then back it out counter clockwise 1 1/2 turn. Then with the engine running and in forward gear, turn the screw counter clockwise in 1/8 turn increments until the engine begins to fire unevenly, due to an over rich mixture. Make sure to allow 10-15 seconds between turns to allow the engine to catch up and adjust. Take note of where this position is. Then, begin turning the screw clockwise in 1/8 turn increments until the engine fires evenly and the RPMs begin to increase. Continue turning clockwise until the RPMs drop off and the engine begins to misfire, due to a mixture that is too lean. Take note of where the screw is at this position. Now slowly turn the screw counter clockwise where it is halfway between the Over rich and Over lean positions. Favor the over rich position. It is always better to run an engine too rich, than too lean.

 

[RickyRegs]

Re: 1985 50 HP Mercury losing power

OK.
Well, after letting it run for a while (even at a reduced power) it became apparent i would need to look more closely so i decided to re-adjust the idle screw to no avail. I did notice, however, that if i squeezed the ball (which was losing its firmness) power would return.
Are we in agreement that it sounds like the tank/fuel line is likel;y the root cause of power loss at this point?

 

[pompeymatt]

Re: 1985 50 HP Mercury losing power

Have you got the baynet style fuel adaptor, male and fem one?

 

[MacDaddy21]

Re: 1985 50 HP Mercury losing power

If your fuel tank and lines are relatively new, they are not your problem. If you squeeze the primer bulb and power returns you need to rebuild your fuel pumps. I bet the diaphragms in your pumps are wrinkled, and the check valves are probably cracking. Rebuild kits are cheap at your local merc dealer