Fuel starvation, New fuel system, Mercury 1500

[Zac Penn]

I have replaced the following...
New fuel hoses 5/16" (previous owner did this 6 months ago) up to a brand new water fuel separator (Sierra 10 microns 90 gph), then 3/8" fuel line up to a brand new primer bulb, through a completely rebuilt fuel pump (diaphragm/check valves/gaskets) then into my three freshly cleaned carbs.
I have removed the gas fill cap, and vent hose from the fitting and blown through the vent hose and there is no restriction because the air come shooting out of the fill hole. I have reconnected the vent hose and blown through the gas fill hole and it comes out the vent screen just fine.

Boat is a 1984 Proline 20 center console and the fuel tank is about 6" below the deck. 5/16" fuel line is about 6' long to the fuel/water filter. The fuel connector on the 1500 is about 14" above the deck, and the top carb is about 33" above the top of the fuel tank.

My problems...
Walk out to the boat and squeeze the primer ball about 6 full times before it gets hard
Don't do anything for about 60 seconds and the bulb is not stiff anymore and requires another squeeze or two
Leave it for 10 minutes and you have to squeeze it 5-6 more times because the fuel has back flowed out of the fuel lines
Put the boat in the water and 1/8 throttle for about 15-20 minutes while you get out of the minimal wake zone and everything is great. Punch it and she rockets out of the hole for about 30 seconds and then bogs because not enough fuel is getting to the carbs. Squeeze the bulb a couple times every 20 seconds and she will scream along just great until you reduce throttle or stop squeezing the bulb.

My tinkering...
Bypass the fuel/water filter and run straight to the primer bulb and everything is exactly the same but you don't have to squeeze the bulb as often. However if you don't squeeze the bulb, she bogs and is starving for fuel.

My diagnosis is that there is just too much of a height difference between the fuel tank and carbs that the diaphragm fuel pump just can't keep up with the demand.

Questions...
Is there anything else fuel related that I have not replaced that could be causing this problem?
Should the fuel be able to back flow out of the lines as quickly as it does?

 

[Dukedog]

try a new OEM bulb and "kit" or replace tha fuel pump...

 

[Jacobsele]

When you rebuilt the carbs do you have old style floats or plastic? new needle/seat? are the floats adjusted correctly?

I had the same issue but it was my fuel line size, I'm still new at this so just tossing some ideas around.

 

[enginepower]

Sounds like 2 problems. Check valve in bulb is bad and letting the fuel travel back to tank but this should not affect the operation. The other is sounds like fuel pump has a torn diaphragm and not pumping sufficient volume

 

[Zac Penn]

My floats were the new plastic kind, but I did not install new needles/seats, I just cleaned everything really well. Both of these items would not cause the issues I am having I don't think.

The priming bulb is aftermarket but only 2 weeks old. The fuel pump diaphragm is only one week old and should be in great shape.

 

[Dukedog]

Squeeze the bulb a couple times every 20 seconds and she will scream along just great until you reduce throttle or stop squeezing the bulb

this leads to one or tha other or both no mater tha age.........

 

[enginepower]

If you squeeze the bulb and it starts running great while you do that, your fuel pump isn't pumping for whatever reason. Make sure the pulse port isn't plugged up.

 

[Zac Penn]

this leads to one or tha other or both no mater tha age.........

Sorry but I am not quite sure what you mean by this.

If you squeeze the bulb and it starts running great while you do that, your fuel pump isn't pumping for whatever reason. Make sure the pulse port isn't plugged up.

I will take the fuel pump off and check the bottom passages for blockage and remove the fittings on the motor to see if anything is plugged up.

 

[Zac Penn]

So nobody thinks that the fuel tank being as low as it is can be causing this problem?

 

[Faztbullet]

The engine being that old has some internal wear and crankcase pressure is likely low. This effects the driving of the pump and fuel flow, to test this take a portable tank and hose and try it, If it works fine you may have to install a Holley red marine pump to help drive fuel to engine. You will need to install a relay on tach wire to turn it on/off.

 

[Zac Penn]

I removed the vacuum pulse lines from the fuel pump and blew into them. Both of them are open but the bottom one was twice as hard to blow into than the top one. Maybe because it was at a different part of the stroke than the upper one? Nevermind I just rotated the crank by hand and the lower one is just as free flowing as the upper one now.

Either way that lower port is way down at the bottom of the motor and I don't know how to remove it without A LOT of work.

 

[Chris1956]

I am assuming you have the single, lower cowl-mounted fuel pump. They must operate at peak efficiency to keep up with fuel demand on those motors. Replace the fuel pump pulse hoses. Some of them had springs inside them to keep them from collapsing. Make sure the pulse hoses do not kink when the fuel pump is installed. Note: Remove the 4 bolts on the rear lower cowling support. That will allow easier access to the pulse hoses.

 

[Jhoppy]

I had a similar problem on my 1350 ended up installing an electric fuel pump and wired it up in such a way as the fuel pump only runs when the engine is running for safety and also when i choke the engine for a prime feature. I'm not sure as to why my on-board fuel pumps were not supplying enough fuel to my engine ether but i do wonder if my pumps were plumed up correctly? When i installed the electric fuel pump on mine i bypassed the on-board fuel pumps but left the primer ball in place to uses as a backup to get me to the ramp when/if the electric fuel pump goes out.

 

[Zac Penn]

Thanks again for the ideas. I have rigged it up temporarily to use a 6 gal fuel tank on top of the deck, plumbed down into my fuel/water separator (to simulate the extra restriction caused by the filter) then through the priming bulb and into the motor. I will water test it like this and see if this helps at all.

If that doesn't help then my buddy gave me another idea that I haven't even mentioned here because I thought everyone would assume
He thinks I could be getting either an air leak or just a clog/restriction from the quick connect/1/4 turn fitting at the base of the motor. He said that has been known to cause problems and if you don't intend on removing the motor regularly, then I should just hard plumb the fuel hose directly to the fuel pump and eliminate the quick connect as a point of issue.

Does that sound like a good idea?

 

[Jhoppy]

It cant hurt to try, you might be able to see a leak at the quick connect when your priming it if it is leaking, but it may only leak vacuum not pressure. my quick connect was new when i converted to an electric fuel pump for the same reason so i know it was not the problem i had, but in hindsight i should have just bypassed the quick connect as you are thinking. I just wonder what your plan is if you do find out that your fuel tank is too low and the motor cant pick enough fuel out of it?? Raise the tank, lower the motor or install an electric fuel pump? I just used a cheap red thump-per type fuel pump 4-7 psi or so i think from the auto parts made by Mr. gasket. They are not the best fuel pumps but that is what i had. It was just an automotive type pump I'm not sure what the difference is in a marine pump?

 

[DavidMoore]

Is the arrow on the bulb pointing upwards (as well as in the direction of flow). If not make sure it is and you will be amazed at the results.

 

[Dukedog]

this leads to one or tha other or both no mater tha age.........

Sorry but I am not quite sure what you mean by this

means either tha bulb, pump or both are bad even if they are new...sometimes a pump rebuild will not "take" no mater what ya do.....tank placement didn't have an impact on fuel feed before tha problem did it? tank has "always" been in tha same place hasn't it?

by-pass tha quick connect and 'lectric is tha way ta go.... but be sure of pressure.. some, like tha Holly's really need a by-pass regulator.. tha cheapies like tha Mr. Gasket don't.. if ya go that route buy 2...with tha 'lectric ya need ta mount it as close and as low to tha tank as possible for best results...those type pumps or more pusher than pullers........

 

[Zac Penn]

Sorry but I am not quite sure what you mean by this

means either tha bulb, pump or both are bad even if they are new...sometimes a pump rebuild will not "take" no mater what ya do.....tank placement didn't have an impact on fuel feed before tha problem did it? tank has "always" been in tha same place hasn't it?

by-pass tha quick connect and 'lectric is tha way ta go.... but be sure of pressure.. some, like tha Holly's really need a by-pass regulator.. tha cheapies like tha Mr. Gasket don't.. if ya go that route buy 2...with tha 'lectric ya need ta mount it as close and as low to tha tank as possible for best results...those type pumps or more pusher than pullers........

No, this is a new install of an old motor on a different boat. The motor was on a fish/ski boat and was probably 10" lower in relation to the gas tank, than it currently is on the Proline.

I tried the bypass and it just didn't work, but I think I have so many splices right now that i might just be creating leaks. I am going to purchase some clear vinyl tubing and connect it into the fuel system tarting at the pressurized side of the fuel pump, so I can see if air bubble are intruding somewhere. If I see air bubbles going up into the carbs, then I will replace the fuel line just before the fuel pump and after the priming bulb and check it again. If I still see bubbles, then I will replace the line between bulb and filter, then check again etc..... I am really hoping that the previous owner didn't leave a hose clamp loose under the deck at the gas tank barb because that is not an easy place to get to with the center console on top of the access panel.

 

[Zac Penn]

No Title

Okay so today was such a pain in the butt!!!!! I installed the clear vinyl tubing in as many places as I could to narrow down where the air was leaking in from. I could have sworn the air was leaking at one point from the fuel pump itself so I went and bought a Mr Gasket 4-7 PSI 35 GPH electric fuel pump and hooked it up to the ignition switch as a short term install to see if that would fix my problem. Well I could still see air in the system so it was time for me to rip out my leaning post and 3/8" Starboard sheet that I had covering the previous owners rectangular hole in the deck (you will see it in the picture)

So once I had that all removed I could access the fuel pickup on the gas tank. I replaced the 5/16" x 1/4" MPT fitting on the tank just to make sure it wasn't the leak, and I ran clear vinyl tubing back to the new fitting and went for my 5th water test of the day. And sure enough I was getting air bubbles (quite a lot of them) coming directly out of the tank. So I guess the pickup tube inside the gas tank has a small hole in it that is allowing air to get sucked into the fuel line.

This actually makes perfect sense now that i think about it, because I had the tank completely full of fuel on the first trip which told me my carbs were clogged up due to poor performance. Once I cleaned them out and reinstalled them I went for a 30 minute water test and the boat performed great. The very next day I took some friends out on the boat and about 20 minutes into the trip I started to have the fuel starvation problem, so I guess the hole is right at the top of the pickup tube.

So how screwed am I??????????
Is there anything I can do to install a new pickup tube without removing the tank from the boat and draining out all the fuel?

The pictures show the hole on the deck from the previous owner, so obviously they were fighting this issue as well but decided not to tell me about it.

 

[Chris1956]

If that cubic-shaped thing in the second picture is the fuel pickup fitting, it should unscrew. The clearance is tight, but with a bit more cutting, you should be able to pull it out, and replace the pickup tube (which is likely rubber). I think you are "in for a penny" with the hole in the deck now....