Fuel bulb sucking flat... got me stumped

[kmagnuss]

Hey guys. I'm getting the oh-so common fuel bulb sucking flat at wide open throttle. Everything up to about 3/4 throttle is fine although it still gets sucked down... but at wide open it actually bogs the engine.

So here's my steps so far:

-89' Action Craft flats boat... bought with a poorly-running 95' Evinrude 115. Boat sat for a year or so before I bought it.
-Put on a 07' Mercury 90 2 stroke carb'd.
-First time out I noticed the fuel bulb getting sucked down even when barely getting up on plane.
-Opened up the fuel cap to see if there was a vacuum in the tank due to a clogged vent. Nothing changed.
-Put on a new, much firmer fuel bulb and blew 15 psi into the fuel lines from the tank side of the fuel/water filter. Could hear the bubbles in the fuel tank when I did this. Took it out for a run and now it will run at 3/4 throttle all day but the bulb still goes flat. Wide open bogs it down after about 30-40 seconds.
-Tonight after being out on the water I replaced the fuel/water filter to see if it helps. I don't really think it will though.

What I THINK is going on is there's something blocking the fuel at the pick up in the tank. The problem is there's no way to get into the tank to clean it out (much). All I have is a hole about 3" across that holds the fuel level sender. I guess I can get my liquid vac from work (I work at a auto shop) and suck the tank out... hoping to get the residue with it... but other than that I really don't know what I should try next. I don't think I have any anti-siphon valves so I've pretty much ruled that out also.

Thanks in advance for your help.

 

[Bosunsmate]

Re: Fuel bulb sucking flat... got me stumped

Hi try taking off the fuel clip and putting the end of the hose straight in the tank, put in one of those cheap inline filters $5 above the fuel bulb if you arent sure the tank is clean.

Those fuel clips at the tank end, both the inlets and outlets can get gunk in them or gaskets falling apart which block them

 

[tazrig]

Re: Fuel bulb sucking flat... got me stumped

If you think your tank is gunked up and plugging your intake hose try Startron:


Star Brite Star Tron Gas Additive - iboats


It will unclog anything that isn't solid like a piece of metal or wood. I used it on my 80 gallon tank and it worked so well I had to keep changing out the carb filters every 2 hours until my tank ran clean. And it starts working real fast, like within a couple hours of pouring it in and running my motors my filters were clogged with what used to be in my tank.

 

[kmagnuss]

Re: Fuel bulb sucking flat... got me stumped

Hi try taking off the fuel clip and putting the end of the hose straight in the tank, put in one of those cheap inline filters $5 above the fuel bulb if you arent sure the tank is clean.

Those fuel clips at the tank end, both the inlets and outlets can get gunk in them or gaskets falling apart which block them

What do you mean by fuel clip? Are you talking about those press on type fuel fittings that go on portable fuel tanks and on some outboards? Like this?

 

[glenn property of pam]

Re: Fuel bulb sucking flat... got me stumped

the fuel line has been changed all the way to the tank? there are cases where the internal rubber in the hose starts to flap around and can cause a blockage. other than draining the tank then giving it a blast of compressed air down the line to blow any junk back in the tank using a cemical cleaner like tarrig surgests might be the best option

 

[kmagnuss]

Re: Fuel bulb sucking flat... got me stumped

Ya know I have heard of that happening to hydraulic lines before... where it will get a little flap in there and everything will be fine for awhile then it will sort of suck itself shut... hmm...

 

[glenn property of pam]

Re: Fuel bulb sucking flat... got me stumped

Ya know I have heard of that happening to hydraulic lines before... where it will get a little flap in there and everything will be fine for awhile then it will sort of suck itself shut... hmm...

along the same lines but with fuel its more to do with the additives they put in modern fuel likes to eat old fuel pipe from the inside out.

 

[Bosunsmate]

Re: Fuel bulb sucking flat... got me stumped

Yep kmagnuss i mean those clips. The rubber grommet that helps seals them can peel back and restrict intake/outflow

 

[CharlieB]

Re: Fuel bulb sucking flat... got me stumped

Or crud accumulation in the dip tube/tank fitting restricting flow.

Something between that primer bulb and the fuel in the tank, is restricting flow so that once demand is greater than flow, the bulb starts to collapse,

This is when the fuel MIXTURE, like the upper carbs, starts getting lean, raising combustion temps and tries to melt down your motor.

Fix it now while it only cost you hoses, fittings, and a bit of time.

 

[kmagnuss]

Re: Fuel bulb sucking flat... got me stumped

Well I finally got around to replacing the fuel line today. First I did the long line between the water separator and the tank... tested it out (the fuel bulb takes a LOOOOONG time to fill after compressing it) and nothing changed. So on a whim I replaced the line between the separator and the fuel bulb... BINGO! I looked in the 2' section of line and the thin plastic liner on the inside of the line had gotten all bunched up and packed in there from the hose barb... I'm amazed any fuel was getting past it.

Now for my first true wide open run to see what pitch prop I need on there.

 

[tazrig]

Re: Fuel bulb sucking flat... got me stumped

Well I finally got around to replacing the fuel line today. First I did the long line between the water separator and the tank... tested it out (the fuel bulb takes a LOOOOONG time to fill after compressing it) and nothing changed. So on a whim I replaced the line between the separator and the fuel bulb... BINGO! I looked in the 2' section of line and the thin plastic liner on the inside of the line had gotten all bunched up and packed in there from the hose barb... I'm amazed any fuel was getting past it.

Now for my first true wide open run to see what pitch prop I need on there.

Just curious was the color of the liner that got bunched up "gray"? I've heard from many people that hoses with the gray liner have had the same type of problem.

 

[kmagnuss]

Re: Fuel bulb sucking flat... got me stumped

The liner was more of a clearish color... but the hose was grey.

 

[tazrig]

Re: Fuel bulb sucking flat... got me stumped

O.K. thanks. I must have gotten my insides and outsides mixed up. Apparently there is something in the grey hose that doesn't like the new ethanol fuels as it seems to get dissolved by it causing blockages like you had. Anyway glad you got it straightened out.


EDIT: found one of the posts I was describing:

Regarding those gray fuel hoses with the special ethanol-resistant liner: The clear inner lining of the gray fuel hose deteriorates over time. (This includes the 2004-2008 Mercury gray fuel lines.) The liner turns yellow. When the clear inner liner deteriorates, it fractures. Pieces of it will migrate down the fuel hose and will wind up at the hose barb by the engine. This results in poor fuel delivery (a fuel line clog) and significant running issues. Usually this is not a major event, usually just poor top end running. But I have seen one Merc powerhead blown up due to lean fuel delivery on all 4 cyls.-probably over a long period of time at max timing and will too little fuel.

 

[MH Hawker]

Re: Fuel bulb sucking flat... got me stumped

I was just going to post about the gray/silver crap fuel line, It got me last year, I had put a new attwood line assy on mine and it never had any thing but real gas ran through it and it still failed.

 

[Texasmark]

Re: Fuel bulb sucking flat... got me stumped

I had a problem with clogging of the Quicksilver gray OEM line after 10 years of service as did at least another person on here. Our residue was tan in color, in small chunks, with a radius on the side....the same dimension as the id of the fuel line. Apparently after several years with current fuels this line degrades and you have this problem. Mine had crud up into the bulb, at the engine interface, in the fuel pump, and clogged the fuel filter.

Mark

 

[smittylv1]

Re: Fuel bulb sucking flat... got me stumped

Mine had a plugged screen inside the fuel tank plastic dip tube. Removed it, replaced lines, bulb and filter....problem solved.

 

[MH Hawker]

Re: Fuel bulb sucking flat... got me stumped

Something like this.

 

[Outsider]

Re: Fuel bulb sucking flat... got me stumped

Remove the anti-syphon valve, run something stiff down the tube to break any screen attached to the pick-up. Don't bother to reinstall the valve, get an elbow. And, NO, it's not required on an outboard with carb/fuel pump above the tank ...