Mercury 8HP 4 Stroke 2012 Stalls Soft Primer Bulb

[Phillip_G]

I have a 2012 Mercury 4 stroke 8 HP outboard with 9 hours of run time on it. The fuel tank is a Quicksilver 3 gallon portable with an Attwood Fuel Demand Valve between the primer bulb and the tank. The outboard runs fine with no misses or noticed troubles except this past week, after a short run across the lake (about 1 mile) at 3/4 throttle, the outboard stalled. I discovered that the primer bulb was soft. Once I pumped it a couple of times, the outboard started just fine and ran awhile again. Before long, it repeated the outboard stall. The tank is in new condition, along with the hoses, bulb and fuel demand valve. The cap has a screw type vent that is open when I start or run the outboard. It has only 9 hours on it and it came new from the factory with the outboard.

This appears to be some sort of leak in the fuel system / tank/hoses/valve but I don't detect any at this point. Any advice? Anyone else experience this problem? Thanks for your help!

 

[blackhawk180]

Re: Mercury 8HP 4 Stroke 2012 Stalls Soft Primer Bulb

I assume it's still under warranty? If so, I wouldn't do much besides take it back to the dealer and have them fix it.
As for the symptoms, it sure sounds like it's not venting properly and starving for fuel but since you are sure you opened the vent screw...? I'm not familiar with the Attwood Fuel Demand Valve but would be suspicious of it.

 

[oldman570]

Re: Mercury 8HP 4 Stroke 2012 Stalls Soft Primer Bulb

If you can borrow a different tank and hose from a freind , try it and see if it solves the trouble. If it dose then you have narrowed it down and can start by replacing the primer bulb and eleminating the demand fuel valve. Make sure that the hose routing keeps the primer bulb in a position that is more vertical with the out flow being the highest , and that the tank and hose are not more than 20" below the carb on the motor. Just a Sugestion to start with , as I have seen some brand name aftermarket parts that are bad and do not get the job done.
Oldman570

 

[Phillip_G]

Re: Mercury 8HP 4 Stroke 2012 Stalls Soft Primer Bulb

I also tried a different fuel tank, hose, bulb with manual venting. The alternate fuel tank had a manual venting system (open the screw on the cap) as opposed to the new fuel tank that came in the box with the Mercury 8HP 4 stroke just 4 months ago. The original fuel tank is pressurized. It does have a screw on the cap that must remain open while outboard is in use but that screw just allows air into the tank as the fuel runs out. The Attwood Fuel Demand Valve (FDV) is *supposed* to provide enough fuel so the outboard doesn't starve or flood. When I tried the different fuel tank, there was no Attwood FDV inline the fuel hose. I ran about 20 minutes across the lake. Anchored, fished for about an hour and a half. When I headed back towards the boat launch, the outboard stalled again at full throttle with a different fuel tank a couple of times.

Yes, the fuel tank is close to level with the outboard and the bulb arrow is always pointed towards the outboard side. I keep it as straight up and down as possible.

So after two different known good fuel tanks, I carried the boat and outboard to the dealer (both under warranty). It's been a week. Maybe the dealer will get to it this next week. They are really busy this time of year. If I get an update, I will share it will all here. Thanks much for the advice. At least I have my bigger bay boat to still fish in. http://forums.iboats.com/images/smilies/joyous.png

-Phil

If you can borrow a different tank and hose from a freind , try it and see if it solves the trouble. If it dose then you have narrowed it down and can start by replacing the primer bulb and eleminating the demand fuel valve. Make sure that the hose routing keeps the primer bulb in a position that is more vertical with the out flow being the highest , and that the tank and hose are not more than 20" below the carb on the motor. Just a Sugestion to start with , as I have seen some brand name aftermarket parts that are bad and do not get the job done.
Oldman570

 

[MH Hawker]

Re: Mercury 8HP 4 Stroke 2012 Stalls Soft Primer Bulb

Sounds like the new and improved EPA fuel cap is to blame. NO surprise.

 

[Silvertip]

Re: Mercury 8HP 4 Stroke 2012 Stalls Soft Primer Bulb

Primer bulbs do not stay firm after the engine starts. Why? Because fuel is drawn through them. So that is not the issue. YOu very likely have a fuel pump issue. If the problem was on the fuel tank side of the system the fuel primer bulb would be sucked flat and it apparently is not. The fact that you force feed the engine by squeezing the primer bulb suggest classic fuel pump failure.

 

[quicktach]

Re: Mercury 8HP 4 Stroke 2012 Stalls Soft Primer Bulb

I'd take it back to the dealer and have him fix it. And have him test run it afterwards.

 

[Phillip_G]

Re: Mercury 8HP 4 Stroke 2012 Stalls Soft Primer Bulb

Not necessarily. As mentioned in the thread, I have tried both the new style pressurized tank and an old style tank with a conventional venting screw. The problem happens with both types of fuel tanks and connectors.

I picked up the boat today after Mercury dealer told me he couldn't recreate the problem. So I will run the boat out at the lake again, and video the whole thing as it happens. Then show him the video. It seems more and more like a random fuel pump problem to me. Will update as soon as time permits.

- Phillip_G

Sounds like the new and improved EPA fuel cap is to blame. NO surprise.

 

[Phillip_G]

Re: Mercury 8HP 4 Stroke 2012 Stalls Soft Primer Bulb

I'd take it back to the dealer and have him fix it. And have him test run it afterwards.

The first time I took it to the dealer for service, nothing was found. I took it back to the river and it would not start at all then. I carried it back to the dealer. The dealer did more diagnostic this time. Mercury Tech found a bad plunger in the carburetor. He replaced the plunger, check valve and a new gasket. The plunger was becoming stuck during operation and that was causing the outboard to act like it was running out of fuel. It was eventually resetting itself. Works fine and starts on first pull again. Thanks everyone for your advice and help!