Merc Fuel System problem

[Diane]

Here's the newest problem!

Hi folks. I’m new to powerboats so be gentle!

My new-to-me 1985 Merc 115hp inline 6cyl outboard is giving me some problems. Last year it had professionally rebuilt carbs, rings, and reed valves. Also has new water pump and propeller. Compression was good. I just replaced all spark plugs and they looked good when I pulled them.

It was hard to start cold and died during idle. I noticed that the bulb in the fuel line was soft during idle and when I squeezed it I saw a loose clamp around a gas line into a carb so I tightened the clamp and the fuel leak stopped. The bulb seemed to stay hard and the motor didn’t die anymore during idle. Yet.

So I took it out and found that under load the motor bogs… won’t get up on plane and acted like it was starving for fuel. When I squeezed the fuel bulb it was soft and the motor immediately picked up and ran fine except that I was alone and couldn’t reach both helm and bulb. So I limped back to my slip.

The gas tank is original, metal, and 15 gallons. Line from there goes to a fuel/water separator, then to bulb, then to motor. I see nothing leaking but that soft bulb tells me something’s wrong with the fuel system.

Could someone tell me how to troubleshoot this one? Should I replace lines? Bulb? Test fuel pump somehow?

Any help is appreciated.

Thanks.

Diane
Ithaca, NY

[Diane]

Here's the newest problem!

Hi folks. I’m new to powerboats so be gentle!

My new-to-me 1985 Merc 115hp inline 6cyl outboard is giving me some problems. Last year it had professionally rebuilt carbs, rings, and reed valves. Also has new water pump and propeller. Compression was good. I just replaced all spark plugs and they looked good when I pulled them.

It was hard to start cold and died during idle. I noticed that the bulb in the fuel line was soft during idle and when I squeezed it I saw a loose clamp around a gas line into a carb so I tightened the clamp and the fuel leak stopped. The bulb seemed to stay hard and the motor didn’t die anymore during idle. Yet.

So I took it out and found that under load the motor bogs… won’t get up on plane and acted like it was starving for fuel. When I squeezed the fuel bulb it was soft and the motor immediately picked up and ran fine except that I was alone and couldn’t reach both helm and bulb. So I limped back to my slip.

The gas tank is original, metal, and 15 gallons. Line from there goes to a fuel/water separator, then to bulb, then to motor. I see nothing leaking but that soft bulb tells me something’s wrong with the fuel system.

Could someone tell me how to troubleshoot this one? Should I replace lines? Bulb? Test fuel pump somehow?

Any help is appreciated.

Thanks.

Diane
Ithaca, NY

[Chris E]

And how do you like boating so far?

Fuel pump is more than likely the source of your delimma. When the bulb goes soft (keep your comments to yourself!!) it is usually the fuel pump. To isolate the boats fuel system try running the boat on a portable tank - If the engine still misbehaves then you'll no where to start looking.

[jkeiper]

Good idea to use a portable tank. Just be sure to open the tank vent or you will have the same problem. I also think it might be the fuel pump because if it was a plugged fuel line or water seperator you would have trouble squeezing the bulb because it would collaps with the suction of the fuel pump. Also be sure there is a gasket between the fuel pump and the crank case. If you have a leak there it won't pulse the fuel pump. Good luck.

Regards,
Jim

[illMATTic]

try having someone pump the primer bulb when it start to cut out. if it runs you know you it is a problem with the fuel. it worked for me. the diaphragm is probably worn out in the pump. i just got a new pump kit for my 115 from rickracers.com. IT WAS ONLY 7 DOLLARS. http://www.checkmate-boats.com/infopop/emoticons/icon_eek.gif i havnt put i in yet. put it looks easy as pie

[Diane]

I pulled apart the fuel lines and found a few problems... crimped vent tube from tank, loose clamps on some fuel lines. So I fixed all that, changed out the fuel/water filter and tested the lines again.. good fuel supply TO the fuel pump. Not so good out of the fuel pump. So I got the kit and rebuilt the pump.... basically replaced diaphragm which had been pretty stretched out, some old gaskets, and screen filter which had been clean. Tested again.. good fuel pressure OUT of fuel pump and the primer bulb now gets hard and stays that way (get your minds out of the gutter).
So.. thanks. Now, once I charge up this battery, I'll go back to my original problem which was hard starting and no low idle. Maybe that'll be techno-magically fixed by the fuel line/pump work I've already done.
Thanks for the help, folks. I'll let you know how it runs when I get it out again in the next couple of days.
Diane
Ithaca, NY

[175checkmate]

I think you fixed the problem. I had the same trouble with mine. I went a different way and by-passed the factory diaphram and got rid of the primer bulb. I installed a electric pump and all the hard start, no idle bogging on take off and only reving to 4k was gone.