8hp 2stroke fuel problem

[S/V Mar-a-Lago]

I have a 8hp 2stroke outboard. The engine starts, but will not keep running. If I squeeze the fuel bulb in the fuel line between the take and the engine every 5 to 10 seconds, the engine runs fine, for as long as I keep squeezing the bulb. If I hold the fuel tank and fuel line higher than the engine 'gravity feed', the engine runs fine.
I suspect a fuel pump issue? Any help with the diagnosis and what I need to do to repair would be appreciated.

S/V Mar-a-Lago

[robert graham]

Sounds like a fuel pump problem...they do wear out..

[scofflaw]

Bad bulb has the same symptoms as well

[S/V Mar-a-Lago]

Re. bad bulb.... I tried using another tank and fuel line (with different bulb) with same results...doesn't seem to be a tank/fuel line problem...also connections seem tight with no air intake issues.

[TownsendsFJR1300]

As we don't have a year or model #, I suspect (as Robert posted), the fuel pump diaphragm has failed.

Remove the pump from the side of the engine and squeeze the primer bulb. If the diaphragm failed, it'll leak fuel and won't pump fuel.

On rare occasions, the bulb "internal valves" can stick close. As yours still runs with squeezing the bulb,, points towards a pump failure..

The pump rebuild kits are cheap.

[Jason2tpa]

Remove the pump from the side of the engine and squeeze the primer bulb. If the diaphragm failed, it'll leak fuel and won't pump fuel.

If the engine remains running while the primer bulb is being squeezed, I also suspect fuel pump failure as noted by others. But I'm a little confused as to your method to diagnose a failed fuel pump, in this particular case.

If a failed diaphragm will leak when the primer bulb is squeezed, wouldn't fuel dump into the lower cowling while the engine is running (and OP squeezing)? He didn't mention seeing a fuel leak, yet it sounds like your suggesting there should be a leak.

What am I missing? Perhaps when the engine is running there is just enough vacuum created to prevent the leak, despite the bad diaphragm?

[TownsendsFJR1300]

If the engine remains running while the primer bulb is being squeezed, I also suspect fuel pump failure as noted by others. But I'm a little confused as to your method to diagnose a failed fuel pump, in this particular case.

If a failed diaphragm will leak when the primer bulb is squeezed, wouldn't fuel dump into the lower cowling while the engine is running (and OP squeezing)? He didn't mention seeing a fuel leak, yet it sounds like your suggesting there should be a leak.

What am I missing? Perhaps when the engine is running there is just enough vacuum created to prevent the leak, despite the bad diaphragm?

Well, you (post #6, bolded and quoted) left OUT the part right before that: quote: " Remove the pump from the side of the engine and squeeze the primer bulb"

As we don't know his model, many pumps are bolted to the side of the cylinder. When the diaphragm fails, fuel leaks into the cylinder crankcase it's getting pulses from. When he's manually pumping, he's filling the float bowl.. .

In his case, it sounds like the diaphragm failed, thus NOT sucking fuel-no leaks. The leak would be visible once the pump is UN-BOLTED and the bulb pumped..

On this particular 8HP :
2006 and Later 8MSH Yamaha Outboard CARBURETOR Diagram and Parts

the fuel pump / diaphram is part of the carb. He's obviously NOT getting fuel to the carb, except by gravity. Doesn't leave much else it could be...



.

[Jason2tpa]

Well, you (post #6, bolded and quoted) left OUT the part right before that: quote: " Remove the pump from the side of the engine and squeeze the primer bulb"

As we don't know his model, many pumps are bolted to the side of the cylinder. When the diaphragm fails, fuel leaks into the cylinder crankcase it's getting pulses from. When he's manually pumping, he's filling the float bowl.. .

In his case, it sounds like the diaphragm failed, thus NOT sucking fuel-no leaks. The leak would be visible once the pump is UN-BOLTED and the bulb pumped..

On this particular 8HP :
2006 and Later 8MSH Yamaha Outboard CARBURETOR Diagram and Parts

the fuel pump / diaphram is part of the carb. He's obviously NOT getting fuel to the carb, except by gravity. Doesn't leave much else it could be...
.

Forgive me, as I'm sure this is remedial for you. Since we don't know his model, let's use mine so I can better understand.

1998 S115TLRW Yamaha Outboard FUEL Diagram and Parts

My fuel pump is bolted to the cylinder crankcase, 2 bolts. It's one outlet bifurcates to each of the 2 carbs. IF the diaphragm failed, yet I could feed the carbs by squeezing primer bulb to keep engine running, would you have me perform the same test of removing pump from case and squeeze bulb to confirm leakage?

[TownsendsFJR1300]

1998 S115TLRW Yamaha Outboard FUEL Diagram and Parts

My fuel pump is bolted to the cylinder crankcase, 2 bolts. It's one outlet bifurcates to each of the 2 carbs. IF the diaphragm failed, yet I could feed the carbs by squeezing primer bulb to keep engine running, would you have me perform the same test of removing pump from case and squeeze bulb to confirm leakage?

Yes.. With the pump un-bolted from the block

You could also look at your fuel filter cup, part #7, and see that it's NOT filling also..

[scofflaw]

Jasons fuel pump can be tested for leakage without even removing it.

While running at idle , pump the primer bulb up hard and keep it hard. If the pumps are leaking they will dump fuel directly into the cylinder. An obvious tone change in engine can be heard and a gas slick in the water from the exhaust can be seen.

[S/V Mar-a-Lago]

S/V Mar-a-Lago here.....

Thanks for the suggestions...the engine year is 2000, the model # 8MSHY...the fuel pump is mounted directly to the side of the carb...the other thing a noticed just prior to the failure of the fuel flowing properly, was that when the engine was tilted up for the night, the next morning it would not start until I pumped the fuel bulb to get fuel into the carb...the bulb was initially soft when I started to pump it, and then would get harder when fuel went through. Does this help at all?

S/V Mar-a-Lago

[boscoe99]

Most primer balls are soft after the motor has been running. The fuel pump creates a low pressure in the primer ball so it is naturally softer than it is when it has been pumped.

If the motor can be made to keep running by pumping the primer ball that is a pretty good sign that the fuel pump is not doing its job.

On a 17 year old motor it stands to reason that the fuel pump might need to be refreshed if it has never been repaired.

Why not rebuild the fuel pump and see what happens? I am guessing it will fix the problem.

http://www.boats.net/parts/search/Ya...TOR/parts.html

[TownsendsFJR1300]

S/V Mar-a-Lago here.....

Thanks for the suggestions...the engine year is 2000, the model # 8MSHY...the fuel pump is mounted directly to the side of the carb...the other thing a noticed just prior to the failure of the fuel flowing properly, was that when the engine was tilted up for the night, the next morning it would not start until I pumped the fuel bulb to get fuel into the carb...the bulb was initially soft when I started to pump it, and then would get harder when fuel went through. Does this help at all?

S/V Mar-a-Lago

The fuel likely ran out the failed diaphragm...

[Jason2tpa]

Ok, let's see if I've completely caught on here. Failed diaphragm. I squeeze the primer, fuel flows unrestricted through fuel pump, into carb bowls, overflows into intake, etc etc, dumps into cylinders. Sound accurate?

Scott...why would the fuel pump need/should be un-bolted from block?

[TownsendsFJR1300]

Ok, let's see if I've completely caught on here. Failed diaphragm. I squeeze the primer, fuel flows unrestricted through fuel pump, into carb bowls, overflows into intake, etc etc, dumps into cylinders. Sound accurate?

Scott...why would the fuel pump need/should be un-bolted from block?

So you can SEE IT vs it gets pumps into the block where you cannot see it..