140 mercury weak fuel pump

VMAX · #1 August 4th, 2002, 07:05 AM

Hi all,

I think I got a few clues the other day about my lack of power problem. When the boat bogs dwn, I touch the choke button and it picks right up for a second. If I keep on tapping the button, the engine accelerates and then finally dies.

Since this seems to indicate fuel starvation, I primed the carbs with the bulb, and then ran a hose from the pump into a bottle and started the engine.

It ran for 20 seconds or so at 1000 rpm until it ran out of fuel, and the amount that pumped into the bottle wasn't enouch to fill all 3 float bowls

(maybe about 3 oz.).

I am assuming that the fuel pump delivery is the culprit, but I don't know what to do about it.

I took the pump apart and found the gaskets, diaphram, and check valves OK, (someone had recently replaced them by the looks of things)

and there is plenty of fuel getting to the pump.

A light squeeze on the bulb pumps a ton of fuel to the pump inlet.

I guess my question is; Is it possible that the primary compression is too low (weak signal to the pump)? I don't know how to verify this, but the engie runs great (50+ mph) when it's getting enough fuel, so I don't really want to tear it down just to improve fuel pump performance.

Are the pumps on these engines just marginal in design (common problem?)

Is there any updated pumps or bulletins that would improve my pump performance?

Finally, if I can't get the pump working well, has anyone out there ever retrofitted another type of pump, possibly electric?

I appreciate any help that you can give.

Thanks, John

12Footer · #2 August 4th, 2002, 07:43 AM

The compression required to operate the pump is the same compression required by the engine, which means you are right on course. Your next step is to replace the diaphram and gaskets with new, and then to check the compression.

If the compression is good on all cylinders, check for a vacumm leak around the intake flange, carb gaskets, or the vaccum supply line to the pump.

But I suspect you'll find a low cylinder, if the fuel pump is in good condition, and getting the volume TO it to pump.

VMAX · #3 August 5th, 2002, 06:30 PM

The compresion is 120 on all cylinders but the hoses look original between the engine and the pump. They had wire ties for clamps (is this normal?) anyway, I'll try a new pump kit and hoses. Maybe they are leaking at the fittings.

I'll use automotive-style spring clamps on the hoses and try again. I'm getting frustrated since I have to drive an hour to the lake, spend $7.50 to launch, and try again. Sure is easier working out an automotive fuel problem (plenty of room to test drive).

Thanks for your help,

John