Fuel delivery problem... thoughts?

[Bc2planker]

Im having a problem somewhere in my fuel line or tank.

I’ve got an 18.5 Campion, with a Honda 115 4 stroke. Then a 15g removable plastic fuel tank under the cuddy. From the tank, the soft fuel line runs to the stern to a water separator, then to the outboard. There is a primer bulb near the tank, and another near the outboard.

The problem is after running at speed for 10-15min, the engine starts to stall and will die if I don't reduce to idle RPM. When this occurs, the primer bulbs stay flat if squeezed. I.e they can’t pull any fuel to re-fill. So clearly the engine is starving for fuel and something is preventing it from flowing. Running at idle or trolling RPM does not produce this problem, it’s only after running fast (3500-4000rpm)

After some troubleshooting, Ive discovered that the only way to ‘fix’ in the moment and get the engine running again is to disconnect/ reconnect the fuel line at the fuel tank end (quick connect). After doing that, the primers work as they should, and the engine will work for another 10-15min running fast.

So it seems there is an air-lock or vacuum happening?

I’ve replaced both the male / female quick connect at the tank, but the problem persists. Ive confirmed the tank is venting properly, I can hear air moving in/out of tank cap vent easily if I push on the tank wall. Removing the cap when the line is not moving fuel does not resolve the problem. I’ve attached pictures of the old and new quick-connects, which I believe are also anti siphon valve.

Wondering what I should try to test or replace next?

 

[Bearded wonder]

What about disconnecting the fuel line at the hose clamp at the tank and putting into a jug/tank of gas. You would then see if it is the tank or not. Do this at every connection. Eliminating parts as you go. I had to do this at the beginning of the year, to diagnose a faulty valve.

Hope this makes sense

 

[Rockfish]

There are lots of threads on fuel supply system problems on this forum worth a read.

It should not be hard to solve.

If it were mine and I was guessing it would be in most likely be in order of likelyhood:

A bad vent --- or partially clogged or in the closed/partially closed position. Run a half filled tank with the filler cap off, if it vents at the cap, and see if that solves the problem. If I had to bet this would most likely be the problem.
I have seen plastic fuel tanks completely collapsed before the motor stalls because the air in vent was left in the closed position.

A bad squeeze bulb pump, they have a one way valve in them. replace it/them, they are cheap or at lest test each one with a new one.

Less likely --

a bad anti -siphon valve,

Crap in the tank that blocks the pick up end/screen and then falls away when you remove the line causing partial intermittent clogging at the pickup.

Some problem with the fuel pump but I doubt it.

 

[Bc2planker]

What about disconnecting the fuel line at the hose clamp at the tank and putting into a jug/tank of gas. You would then see if it is the tank or not. Do this at every connection. Eliminating parts as you go. I had to do this at the beginning of the year, to diagnose a faulty valve.

Hope this makes sense

Thanks. I was thinking of doing just that as a next step... I have another small tank I can use. Just figuring out how to run with out a cap and without splashing fuel around.

 

[Bc2planker]

There are lots of threads on fuel supply system problems on this forum worth a read.

It should not be hard to solve.

If it were mine and I was guessing it would be in most likely be in order of likelyhood:

A bad vent --- or partially clogged. Run a half filled tank with the filler cap off if it vents at the cap, and see if that solves the problem. If I had to bet this would is most likely be the problem.
I have seen plastic fuel tanks completely collapsed before the motor stalls because the vent was left in the closed position.

A bad squeeze bulb pump, they have a one way valve in them. replace it/them they are cheap or at lest test each one with a new one.

Less likely --

a bad anti -siphon valve,

Crap in the tank that blocks the pick up end/screen and then falls away when you remove the line causing partial intermittent clogging at the pickup.

Some problem with the fuel pump but I doubt it.

Seems like a good list.

I've already tried removing the cap, didn't solve the problem, so I don't think its a vent issue.
The problem did start occurring after I did some work on the tank, so there is a possibility there is some junk being pulled against the pickup screen. I'll look at that and some old threads on the topic.
Cheers.

 

[Rockfish]

Seems like a good list.

I've already tried removing the cap, didn't solve the problem, so I don't think its a vent issue.
The problem did start occurring after I did some work on the tank, so there is a possibility there is some junk being pulled against the pickup screen. I'll look at that and some old threads on the topic.
Cheers.

If you messed with the tank make sure the end of the pickup is not jammed up against a surface in the tank or the pick up is not partially clogged or restricted in some way. It does sound like poor venting though.

I have also seen problems with line components with valves being installed backwards if you replaced any recently, especially the squeeze bulbs - they have a direction arrow on them. I guess the fuel line itself could be partially clogged some place or partially compressed. Fuel filters good?

 

[casper5280]

What's the reason for the 2 pump balls? That may be the reason right there. One pump ball should be more then enough

 

[Bearded wonder]

Ye

Thanks. I was thinking of doing just that as a next step... I have another small tank I can use. Just figuring out how to run with out a cap and without splashing fuel around.

yeah I smelled like gas for a while after fixing mine. Maybe try a clean 2L pop bottle. Smaller opening, maybe less gas will spill out.

 

[Rockfish]

What's the reason for the 2 pump balls? That may be the reason right there. One pump ball should be more then enough

Very good point.

However, I do run two pump balls in line and some supply systems can work that way, especially if it is a tight supply system with no micro air leaks. In our case there is a pump close to the motor up high used as needed (almost never) most of the time and one close to the tank on the keel line which is a little more difficult to access. It is a long distance and lots of components and elevation between the built in keel tank and the motors way out the back on the large pod. The reason for the ones close to the tank is that it makes it very easy to charge the whole system when it is dry or the Racor bowls are empty when the filters are replaced. In our case just one pump high close to the motors seemed to struggle to do that with an un-primed system.

I messed around once with filling up and installing the external Racors bowls with a small gas tank while splashing gas around the bilge and it was a pain. The extra pumps close to the tank pushing gas into the system makes it easy. I had intended to remove them once the supply system for both motors was charged, but in our case both motors run great with the 2nd pump in place so I have left them in place for future fuel system charging convenience. I know that can cause problems but in our case it has not. We monitor them and I know having two pumps per line can increase the chances of micro sucking air leaks with 4 additional clamps and also adds some added fuel flow restriction and it is an additional component that can fail. In most cases having two inline pumps should be avoided but it seems to be working so far in our specific application. Our whole fuel supply system and Al tank was replaced not long ago with high end components and clamps and is very tight. If the extra pumps ever cause a problem, they are gone.

 

[Original]

I have seen the inner lining of a grey fuel line separating and collapse on itself restricting any fuel flow. Trying another tank and line should get you going.

 

[Bc2planker]

What's the reason for the 2 pump balls? That may be the reason right there. One pump ball should be more then enough

Not sure, had two when I purchased the boat. It’s a fairly long run from the tank in the bow, to the separator / engine. One bulb is on the tank end, before water separator, the other after the separator near engine. Twice as many connections... twice as many opportunity to leak air in...

 

[Bc2planker]

So Murphy’s law in full effect today. I went out and bought all new lines, bulbs, connectors, etc. Then out on the water to run it and try to isolate the issue.

Ran for 40 minutes, some at full throttle 5000rpm, 33knts, and the damn thing ran perfect!

I’m pretty sure it’s either a micro air leak at the tank end, or perhaps junk clogging the intake filter in the tank. But being intermittent, makes it even more fun to figure out!

Thanks for the replies so far...

 

[Bc2planker]

I have seen the inner lining of a grey fuel line separating and collapse on itself restricting any fuel flow. Trying another tank and line should get you going.

I’ve read that too... will replace the line if it come down to that, hack the old one up to peek inside.

 

[Rockfish]

So Murphy’s law in full effect today. I went out and bought all new lines, bulbs, connectors, etc. Then out on the water to run it and try to isolate the issue.

Ran for 40 minutes, some at full throttle 5000rpm, 33knts, and the damn thing ran perfect!

I’m pretty sure it’s either a micro air leak at the tank end, or perhaps junk clogging the intake filter in the tank. But being intermittent, makes it even more fun to figure out!

Thanks for the replies so far...

You may have fixed it. It could have been as simple as a bad bulb pump going flat over time as you ran it, and choking off fuel.

 

[Fish Camp]

I have seen the inner lining of a grey fuel line separating and collapse on itself restricting any fuel flow. Trying another tank and line should get you going.

Another line not big enough for flow of fuel. primer bulbs still not to be able for of collapse .try adding another layer mesh to line.watch for bulbs at WOT. Stop restricting flow and remain integrity of the line and bulb. o O

 

[Bc2planker]

You may have fixed it. It could have been as simple as a bad bulb pump going flat over time as you ran it, and choking off fuel.

That’s the thing, I didn’t actually change anything, just bought parts and was going to swap out one at a time, but couldn’t reproduce the problem today. Huh

 

[Unreel]

Had a similar issue with a built in tank, ended up being junk floating at the bottom of the tank would clog up the pickup after 15 20 minutes of running.