91 Mercury 115 Primer bulb losing prime

[huggyb1972]

Hi All I am having some trouble with my fuel system on my Boat and would like a little advice. The boat is a 1990 Spectrum 1950 Sportsman. Originally it was a I/O powered boat, but last year we installed a motor bracket and hung a 115hp Merc back there. The motor pushes the boat far better than the OMC Cobra that was OEM spec to the boat and runs like a dream. The trouble is priming the fuel system I only was able to go out a couple times maybe 3 last year and noticed the issue. This year I grabbed a new primer bulb, But forgot it on out 1st cruise out which other than the 1st startup on the trailer it ran flawlessly. Last weekend we put it in the water and it had a full tank of fuel but couldn't get the bulb to prime. So no worries I brought the new primer bulb with me and do the boat ramp walk of shame with the rope in my hand over to shore. Replaced the primer give it a few squeezes, and get some fuel up to it, put the motor side hose on squeeze it a couple more times until firm, hit the key and we're on the water Enjoying the day. The next start after the motor had been off for about a hour I had to loosen the Motor side hose again to to prime it with fuel. I'm loosing prime somehow but I'm not leaking fuel or anything obvious.

How should my fuel system for the outboard differ from the I/O that was previously there? The tank is a 20ish gallon aluminum below deck center mounted tank. The vent allows fuel to spit out upon a full tank so I don't believe it''s obstructed. The fuel hose to the motor is less than 8ft long and theres probably at or a little less than 3' difference in elevation from the tank to the motor fuel connection. Eventually I'm going to Hang a new 4 stroke outboard back there like maybe a Suzuki 140 or a Yamaha not sure yet I just want no trouble. thats all.

 

[racerone]

The bulb does NOT need to stay hard once motor has started !

 

[huggyb1972]

Agreed and that I get. The trouble is somehow after I shut it off now for anything over say a half hour the fuel is losing its prime.

I am concerned about the foot valve on the tank. Is there a different one for a outboard power and a I/O?

 

[achris]

...I am concerned about the foot valve on the tank. Is there a different one for a outboard power and a I/O?

Anti-siphon valve? No, same for outboard or stern drive.

How is the primer mounted? Fuel flow face 'uphill' or down, or laying flat?

The other possibility is an air leak in the line somewhere between primer and tank. Use a section of clear hose (after the primer) and observe it while the engine's running. You shouldn't see any air bubbles.

Chris.......

 

[huggyb1972]

I would say it's laying flat mostly. I was concerned that maybe the anti syphon valve was wrong for my application. It could be going bad I suppose. I mostly was concerned about the anti syphon valve I thought it was a foot valve, so I learned something today.

Now my fuel pump was always above the tank and still is by quite a bit more now do even need the ASV?

 

[achris]

If you have any part of the fuel line that is below the top of the tank, or could be if the line broke, or the fuel pick up comes from the bottom of the tank facepalm: yes some do), then you should have an ASV...

 

[huggyb1972]

Alrighty then. I'm just gonna replace all the hose for the fuel supply and the ASV. It's got to be something simple the motor runs to good otherwise. I've got a tip planned to SC later this year so we can't have any hiccups. Especially down there.

 

[Texasmark]

Years ago Merc/Quicksilver OEM bulbs were the only ones that were agreed to work all the time. The little football shaped thing was a loser.....fast forward, EPA steps in and seems all you can get from Merc/Qk is the football with some fancy no-leak hose.....as if fuel lines of the past leaked anyway....considering there wasn't any PSI to force leaking....know not of anything inside before or after, with either.

I do know that a check valve is required between the bulb and the tank to force the fuel to to toward the engine when squeezed and allow fuel to be sucked up from the tank when flat and relaxed.

I just bought a new EPA approved hose/bulb assy, Merc./Qk and it has the football, paid like $30 for a 3' POS. It wouldn't hold prime so I said !@#$%$, went on ebay and bought a 5/16" (my fuel line size) aluminum cased, check valve and installed it between the bulb and the tank for about 6 bucks. Problem solved!

 

[huggyb1972]

Alright got everything working right again. I don't have the ASV in there any longer. I bought 10' of hose and a Mercury printer bulb. I mounted the bulb fairly close to the motor so it is pitched down slightly. Never had one trouble priming or starting Friday.

It got me to thinking though i could add a small diaphragm pump mounted down by the tank that I could use to prime the fuel system. I have a boat that used to be an I/O so I have a rather large swim deck that I have to crawl over to get to the primer bulb. Is that something that has been done? Are there any rules I should follow? The pump would be a low pressure pump probably 2-3psi.

 

[Texasmark]

If you install the aluminum check valve, the hose will retain fuel. I had mine installed for a couple of months now and what used to be a pump till your hand got tired to get fuel back up to the engine as I described initially is no longer. When I get ready to start the engine, the bulb is now soft (still partially containing fuel...like is the case when the engine is running and you shut it off) and only takes a couple of squeezes to get hard. Problem solved!

https://www.ebay.com/itm/2x-3-8-10mm...72.m2749.l2649

This for a ⅜" fuel line. If yours is 5/16 the same supplier sells them too on ebay. Ensure you pay attention to the arrow marked on the side when installing and obviously it goes between the bulb and the tank. I put mine about 2" from where the permanently mounted fuel line exits for attachment to the 3' flexible hose-bulb assembly that connects to the engine.