Motor issues

[crappiencali]

My buddy has a 40 horse mercury that wont run very well. When we first get out to the lake and start it it runs really rough then stalls out. Then when we get it running and give it throttle she'll go then lose almost all her power. Then when we put the motor back into neutral it stalls out and them almost impossible to get started again. We check the fuel lines, the spark plugs, the fuel in the tank is new. Do any of you have any suggestions on what could be the problem? Any help would be greatly appreciated.

[Basstex]

You might give the iboats forum a try, they helped me with my Merc.http://forums.iboats.com/cgi-bin/ubb...ubb=forum;f=29

[lebruce]

Does the 40 have oil injection on it ? It sounds like the problem I had last year on my 96 -40hp.It started hard and ran rough.Then once you got going shed run hard for about three city blocks at full throttle then lose power like you were running at 1/4 throttle,then die when placed in neutral. I discovered the oil line between the oil pump and the check valve was broke and this in return let me know my low oil alarm didn't work also . The way I discovered this ,I took the fuel line off at the carb and put in a clear glass turned the motor over to pump gas in the glass and seen no oil present.I thought the oil pump might have gone bad then but it was just the line had broke.

[smedley]

What year is the motor?

I have an older ('82) Merc 40 hp that was doing exactly the same thing. My problem was the idle mixture screw wasn't set right. Here's the way my manual says to set it:

Turn the screw clockwise just until seated, then back it off 1 1/2 turn.

You must have the boat in the water to make the next adjustment. Don't try to do it with the muffs on it. It will not be the correct setting.

1) let the motor warm up to operating temp
2) put motor in gear to a point where it would normally be at idle speed
3) Turn the idle mixture screw until the motor runs smooth and rpm's begin to increase. Mark that spot.
4) Continue to turn the screw clockwise until the engine begins to misfire. Back it off to halfway between that point and the first point.


If this doesn't work....look at the fuel pump. And, I know it sounds stupid, but make sure the vent is open on the gas tank.

[Woohdog]

It might be a seal. Have you noticed an oil slick on the water around the motor?

[jfraley]

Motor problems suck, especially when you find them on the water.

[stray]

If this problem just accrued and you said the fuel is new, did you all just fill it up? If so you may want to check the vent on the gas tank cap. I did that once, filled the tank on the way to the lake tighten the vent, got on the water and the boat wouldn’t run or wound for a little while then die. I’ve found to check the simple things first.

[Barnacle Bill]

That is typical of a bad diaphram in your fuel pump. Cheap and easy fix on most motors. You can verify it by starting it up and when it starts to die, keep pumping the primer bulb. If it wants to keep running, thats your problem. If the tank vent is closed or clogged, the bulb will collapse while the motor is running.