fuel filter and primer bulb questions

hwindle

Seaman Apprentice
Joined
Aug 4, 2012
Messages
34
I have a 25 4 2003 Mercury, that sat for around 8 months. It ran perfect before, and cranked up and seemed to run fine last weekend. However, after taking off and getting on plane, it died like it ran out of gas after less than a minute on full throttle. I pumped the primer bulb, and it started right back up again. We then trolled for an hour with no problems, but when getting on plane again- it died after a few seconds. Classic example of a clogged fuel filter it seemed.
The one strange thing is when I pump the primer bulb, new last year, it didn't want to expand back out right away, which I took as it was having trouble drawing fuel through my spin on fuel/water separator. I replaced this filter when I got home, and when I dumped the gas out of the old one, it wasn't perfectly clear, but it didn't look that bad, and I saw no evidence of water or sludge. I filled the new filter with gas, put it on, and tired to prime the carb again. The primer bulb again didn't want to fill back out right away, and now the motor wouldn't run. A small spray of ether cranks it immediately.
I took out the drain screw on the bottom of the carb, and only a little gas came out. I removed the fuel line from the fuel pump so it was going directly to the primer bulb, and when pumping I would get a little squirt of gas- but mostly air. Several pumps later, it was still doing the same thing, no stream of gas and the bulb takes a minute to get full again.
The gas tank is plastic, and built in. I think there must be some junk somewhere restricting the flow to a trickle, enough to idle but not run. My questions:
1. If the primer bulb squeezes right, but doesn't fill back out right away- doesn't that mean it can't draw fuel in?
2. If I blow air through the spin on filter, should I go from the inlet side, or backwards from the outlet side, to try to blow out possible crud?
3. If I blow air from the inlet side of the filter back towards the gas tank, it should bubble in the gas tank and have no restrictions, right?
 

Nathan Bond

Seaman Apprentice
Joined
Jun 28, 2014
Messages
45
You may have a restriction in your fuel tank. It could be either an anti-siphon value that isn't opening correctly, or perhaps something in the tank blocking the fuel screen. May be a blocked vent, as well.
 

herdsman

Cadet
Joined
Jun 30, 2014
Messages
8
Take the cap off the fuel tank and try the same things again - if that solves the fuel delivery problem then you have a blocked vent.
 

hwindle

Seaman Apprentice
Joined
Aug 4, 2012
Messages
34
I fixed it, but I don't know exactly where the blockage was at. At this point, I am happy. I do not believe it was the tank vent, since it had a half tank, and so had a lot of air. I did blow out the vent in the filler cap, but couldn't see anything come out. I blew air into the tank from the inlet of the fuel/ water separator, and it did pressurize the tank, as when I took the air hose off gas blew out. I don't think the vents are meant to handle that much air flow.

I fooled around for an hour yesterday and found nothing that made sense. My vacuum pump showed 15 in at the gas inlet to the fuel pump, not good. But everything I took off was clear individually.
I did find out the answers to my original questions though, if it would help the next guy:

1. If the primer bulb squeezes right, but doesn't fill back out right away- doesn't that mean it can't draw fuel in?

Yes. That is what mine was doing, and when disconnected from the inlet, it immediately filled back up. Once I fixed things, it did it with fuel. So if your bulb doesn't fill back after a squeeze, the problem in on the inlet side.

2. If I blow air through the spin on filter, should I go from the inlet side, or backwards from the outlet side, to try to blow out possible crud?

I blew it through the inlet side, even though my vac pump said it was having no restriction. It may have/or not been something that fixed it, but it didn't hurt.


3. If I blow air from the inlet side of the filter back towards the gas tank, it should bubble in the gas tank and have no restrictions, right?

Yes it did, as well as I mentioned, pressurize it.

After seeing no obvious crap come out of anything, putting it all back it started working normal. My primer bulb shot a full stream of gas out of the inlet to the fuel pump, and got hard and filled up immediately when pumped when i hooked it back up. Motor started right up.

I suspect there must have been a little piece of crap blocking a hole somewhere. I never did see the dreaded sludge of ethanol/gas. The true test is out on the water, but the at home running is back to normal.
 
Top