Fuel Starvation Problem

[BMAC1988]

just got back from our river ride today and looking for some input. this is the first ride in about 6months and the first ride since Ive made the new additions. the changes made on the fuel system were I changed the never before changed fuel filter/water separator and I added a GFS10 fuel meter.

first half of the day went great with absolutely no problems. then all of a sudden it started bogging. while checking my fuel flow it would go from 6GPH cruising then drop down to 5-4-3-2-1-0 and the motor would die out. I found out that if I let my girlfriend steer while I stayed back at the back and watched the fuel meter and when it started to drop i could pump up the fuel bulb and it would "catch" and go fine for a while. I thought no problem, fuel pump is probably going bad (never been changed). then the bulb-trick stopped working and the bulb would squeeze then stay sucked in. I figured the pickup in the tank was picking up and clogging with trash. so I took a line loose and blew backwards thru the line to remove any debris. that worked great for the motor shutting off while driving, but it will still seem to "loose prime" when I shut it off and crank it back up.

I don't know if its a fuel line problem getting air in the system somewhere, I cannot find any leaks. or a maybe a fuel pump going out, that hasn't been changed but think im going to just to be safe. or maybe trash in the tank, weve owned this boat for about 15yr before it was given to me and NEVER had a problem with trash in the tank (like I said the fuel filter had never been changed).

[MarshMarlowe196]

I would check that the fuel/water separator is making a good seal on the mount.  It could be sucking air, which could explain your symptoms.

Past that, the first thing I'd do is run the engine on an external tank with a new hose and bulb to determine whether the problem lies in the engine or the boat fuel supply.

[LiquidTherapy]

If the bulb is sucking flat there is a restriction tank side. Vent, check valve/pickup or even a collapsed fuel line. Or that walmart bulb sucks. The bulb going flat should be a bad bulb or a restriction. If you have a poly tank the tank mite be colapsing an making pickup hit the bottom causing a restriction. Just a thought or three

[fitz73222]

Sounds like venting to me. Temporarily run the boat with the gas cap removed a see if the problem goes away. If it does look first at the screen on your external vent to make sure mud dobbers or spiders haven't set up house over the screen openings. They love my vent! Could also be a sticking check valve in your primer bulb, or fuel line collapse from ethanol degrade. I've seen fuel lines completely chrystalized internally and pieces of the fuel line block fuel flow. Try running a remote 6 gallon tank and different fuel line as Marc suggests and see how she runs if it fails the gas cap test

[fitz73222]

As Jessie suggests!

[BMAC1988]

thanx guys. I tried removing the gas cap to see if there was a vacuum on the tank while on the water and there was no difference. ive already ordered a new gas line and primer bulb. ive also got a new sender from WEMA coming to make my fuel gauge work. when I get into the tank im going to try and remove the pickup as well as clean out the tank with a shop-vac. im also going to change out the new fuel filter with another new one and change out all the fuel line with new.

im still stumped to why it is loosing prime when i shut it off. maybe its got an air leak at the quick-disconnect letting air in??

[fitz73222]

That wouldn't make the bulb go flat plus usually if you have an air leak you usually have fuel dripping along with it.

[BMAC1988]

very true. the bulb stopped going flat after I removed the line and blew back thru to the tank, it would pump right up.

I just remembered that at the end of the day when the boat was running good I wanted to do a full speed run while playing with the trim tabs and motor trim to see if I could gain some top speed. after about a minute of WOT the "fuel flow restriction" alarm went off.

[BMAC1988]

well got to messing around with it today. figured since I have a new sender coming and I wanted to look at the pickup tube anyways, I might as well pump all the fuel out. so I just rigged up a CARTER electric fuel pump and took the fuel line right where it goes into the motor loose and put it on the  electric pump. I was going to watch the fuel and see when/if it started to plug up and cut off the flow then move back in the line past each component (bulb, fuel flow meter, filter, etc) until the restriction was no longer there.

so I started at the line right on the motor and turned the pump on. I also turned my chartplotter on and check fuel flow to see what it did......
 

it stayed at 47gph thru the remaining 18gal of gas in the tank without a hiccup. guess that narrows it down to the fuel pump??? but I still don't understand why the bulb was staying sucked down.

[Capt. Bob]

I'll guess.

1: On its best day, your engine's fuel pump could never reach that level.

2: Since it can't pull with that much suction, it could indicate debris in your anti-siphon valve.

Check and see if you have one on your tank. It's cheaper than a fuel pump.

Just a thought.

[BMAC1988]

where is it at? and what can I do to check it, or should I just remove it

[Capt. Bob]

Here's a recent thread concerning same.
viewtopic.php?p=124995#p124995

Read through the thread and you get a good idea of where to look on your model. Hopefully you will have enough access to work on the pick up. Post a few pics for future reference if you have an opportunity.

Thanks and good luck.

[BMAC1988]

thanx Bob. I know that my fuel pickup looks exactly like that one WITH the fuel shut off. ill have to check into that anti siphon when I get time to dive into it. ive got a new fuel pump coming (only 50 bux from ebay) so I think its good insurance either way since its never been changed, far as I know.

assuming I have the anti siphon, do I have to remove the pickup from the tank itself? when i get the shutoff off is the spring right there and can be pulled out with small pick?

when i was trying to get it working on the water i did remove the fuel line and blew on the line back thru to the tank. the first time it seemed like it was stopped, but the second time i could hear it bubbling in the tank. since i was able to blow nto the tank would that mean that i don't have an anti-siphon device?

[Capt. Bob]

assuming I have the anti siphon, do I have to remove the pickup from the tank itself? when i get the shutoff off is the spring right there and can be pulled out with small pick?

Mine was in the "el" so you should find it there (if one is there).
I did not remove the pickup from the tank so IIRC yes, you can pull it out once you have the "shut off" valve removed (again that's assuming you have room to work). I can't remember the exact procedure but I believe you can pull it out with a "pick" of some sort (the end of the spring) and then the ball will come out.

since i was able to blow nto the tank would that mean that i don't have an anti-siphon device?

Yes, no, maybe.....

I believe the device works in this manner but don't hold me to it.

The ball resides on the upstream side of the "el" (closest the tank) with the spring applying pressure opposite of the fuel flow. By design, the spring exerts enough force to keep the ball sealed against the opening in the "el" to prevent the flow of fuel if the fuel line should become detached and fall to a point lower than the fuel level within the tank. It is designed to prevent the siphon effect that would occur in that type event. The fuel flow in this case isn't strong enough to depress the ball against the spring so the hole stays blocked.
 
The fuel pump draws fuel from the tank and this flow presses the ball downstream thus allowing fuel to flow through the once blocked "el", flow around the ball and exit the "el's" downstream side (fuel line attachment). The spring compresses and applies pressure opposite this flow preventing the ball from lodging against the downstream opening and greatly reducing the fuel flow (the ball is slightly smaller than the downstream opening, that's how it's installed). When the motor is at rest, the spring (by design) will apply enough pressure to hold the ball in its original place and again become an anti-siphon device.

All this works great as long as the fuel is clean but once debris gets caught up in the mechanism, the flow is degraded and it could be causing your problems. It would also explain why you could blow back into the tank if the debris is somehow lodge in the mechanism and not allowing the spring to seal the ball against the opening it's designed to seal.

These are just thoughts as to why this might happen and you may indeed not have this valve but rather have a blockage at the bottom of the pick up tube.

If I'm wrong with my logic on how this device works, let's hope someone will step forward and explain. I'd really like to know too.

Good luck.

[BMAC1988]

ok makes some sense. i thought it was just there to keep the motor primed with fuel so it was easier to crank since it wouldn't let fuel drain back to the tank after the engine was shut off. I very well may have one now that you mention how it works... while I was starting draining the tank I was going to just let the line off the motor drain into a can thru a siphon that id create by using the primer bulb. it would pump fuel with the bulb but soon as I stopped squeezing the bulb fuel flow stopped. this is when I rigged up the electric fuel pump contraption.