F60tlr Air in Fuel Line

[TcjMiami]

I have a 2006 F60TLR with 225 hours on the motor.
I have an issue where the motor is shutting down at low speed with air in the line.
I have replaced the Fuel line, primer ball and engine fuel line connector.
The tank end is a barb.
The tank is a 20 Gallon plastic that was cleaned and inspected 6 months ago.
I have confirmed that the pickup tube is good and have removed the check valve at the tank.

I also bypassed my external fuel filter water separator.

I am seeing the primer ball get soft whenever the motor is running and have seen air in the fuel filter on the rear of the motor.

Should I replace the fuel pump, it seems to be working and when I replace the inline strainer on the motor it sprays a little fuel.

Thank you so much for your information.

Tom in Port Charlotte.

[Jason2tpa]

I have an issue where the motor is shutting down at low speed with air in the line.

Describe "shutting down"...meaning it completely cuts off?...slowly loses rpms despite no change in throttle?

I am seeing the primer ball get soft whenever the motor is running

Once the engine has started and is running, the primer bulb no longer remains firm. This is normal. Wrap your hand around the primer bulb while in gear above idle and feel the flow of fuel through the bulb. If you're not feeling flow around the rpms when the engine shuts off then its a good indication your fuel pump is failing.

and have seen air in the fuel filter on the rear of the motor.

The fuel system is an "open air" system, hence the primer bulb. When you start engine for first time of day you squeeze the primer bulb, right? With this action, fuel drives air from the tank to the pump. A diaphragm type fuel pump cannot create sufficient vacuum to draw fuel from the fuel tank during cranking. It needs the crankcase pressure to function. Small air leaks in the fuel line, between the pump and the tank, will dramatically reduce fuel pump efficiency and fuel flow volume.

I don't believe seeing air in your fuel filter is the cause of the issue. However, you should triple check all connections and check for fuel line punctures to be certain.

Should I replace the fuel pump, it seems to be working and when I replace the inline strainer on the motor it sprays a little fuel.

Fuel pumps usually do not just go completely dead, they tend to fade out before complete failure. Diaphragms loose their tension, check values stick, etc. You've replaced everything except the fuel pump. And if you're fuel pump is failing, all of the new fuel components you replaced matter not.

[TcjMiami]

The motor runs fine until it completely shuts down (as in no fuel).
You can then restart it after pumping the primer ball.

The motor will remain running if you keep pumping the ball.

I have checked everywhere in the fuel line and do not see any leaks under pressure running or not.

I will try the pump now.

It is the old story.
The last thing you check is always the issue.

Thank you for the response.

TOM

[99yam40]

if it is an air leak it will be in the suction side of the pump, so you will not see fuel leaking because it is not under pressure

You can check fuel pump pressure and vacuum with the proper gauges and you can install a clear piece of tubing for testing to see if air is being sucked in,

[Jason2tpa]

A diaphragm type fuel pump cannot create sufficient vacuum to draw fuel from the fuel tank during cranking. It needs the crankcase pressure to function.

Essentially, with a perfectly operating engine and engine systems, the fuel pump operates when the engine is running. Now that you have a better understanding of how a fuel pump operates, read your own words below. I believe you have already discovered the cause of the engine cutting out.

The motor will remain running if you keep pumping the ball.

Coincidentally, troubleshooting a potential fuel pump problem is to do exactly what you said you did above: does the engine remain running while squeezing primer bulb. Yes it does! Which means you squeezing the bulb is taking over the function for the failing fuel pump, thus allowing the engine to continuously receive fuel. Stop squeezing bulb, engine stalls due to not receiving fuel.

[TcjMiami]

Thank you for the help.

I was just trying to rule out all possibilities and yield to those with more experience I have already bought a pump and will try it next weekend.


Thank you again for your help.

TOM

[TownsendsFJR1300]

You didn't happen to have the under cowl fuel filter off or do any work to the boat engine/fuel system/ fuel filter PRIOR to the issue, correct?

[fairdeal]

A diaphragm type fuel pump cannot create sufficient vacuum to draw fuel from the fuel tank during cranking. It needs the crankcase pressure to function.

Interesting, did not know that, on a four cycle engine, crankcase "pressure" had an effect on the fuel pump.

I thought it was simply the camshaft (or other revolving engine part) producing a repeating mechanical motion which pulsed the diaphragm.

[boscoe99]

Interesting, did not know that, on a four cycle engine, crankcase "pressure" had an effect on the fuel pump.

I thought it was simply the camshaft (or other revolving engine part) producing a repeating mechanical motion which pulsed the diaphragm.

You did not know that because that is not the cause.

Methinks someone is confusing a two stroke pulse type fuel pump with a four stroke mechanically activated fuel pump. A two stroke fuel pump pumps fuel any time the motor is turning over. Cranking or running. Positive and negative pressures are created as the piston goes up and down. Those pressures act on the fuel pump and cause it to do its magic.

[boscoe99]

On the other four stroke hand

[TcjMiami]

I do appreciate the the feed back and documentation.
I was actually a factory auto mechanic a million years ago and just double checking do to a lack of experience in the modern hardware.

This forum is great the the depth of the discussion / analasys is really impressive.



TOM

[TcjMiami]

Saga continues

I have replace the following:
Fuel line
Priming Blub (twice)
Fuel fitting on Line (Twice, Currently using an OEM)
Fuel Fitting on Engine where fuel line attaches.
Seal in Fuel Filter.
Fuel Filter
Fuel Strainer (After Fuel Pump)
Fuel Pump

I even used a temp tank two feet above the motor that feeds gas by gravity.

The air still come back into the system particularly at low speed.
I am going to add a fuel pump by the tank unless some one has a better idea.

TOM

[rodbolt17]

my suggestion?
find and fix the problem.
a simple vacuum guage will help.
if the pump is known good aand by pumping the primer bulb keeps it running I would look for an airleak.
at every joint place a few drops of two stroke motor oil.
see if it gets drawn into the system.
if it does you will see it dissapear and discolor the fuel.

I don't recommend any type of external pumps and in the US it would most likely violate USCG regs.

[TownsendsFJR1300]

Following your train of thought RB, what might be easier and should work at least from the engine forward:

Remove the fuel line at the engine, gently pressurize it (maybe 15 PSI as it's going to bleed out in the fuel tank) and squirt all connections, filters, etc with soapy water looking for bubbles.. I would think it'd be easier.

Also, check the smoothness of the transom fuel filter GASKET SURFACE (and no extra filter o-rings). If there's a bunch of corrosion on the fuel filter mount, could be from there as well...

[Jason2tpa]

my suggestion?
find and fix the problem.
a simple vacuum guage will help.
if the pump is known good aand by pumping the primer bulb keeps it running I would look for an airleak.
at every joint place a few drops of two stroke motor oil.
see if it gets drawn into the system.
if it does you will see it dissapear and discolor the fuel.

I don't recommend any type of external pumps and in the US it would most likely violate USCG regs.

As a guy who spent years in college/career practicing flow dynamics, I can back up rodbolts suggestion of performing a vacuum test. Your fuel pump, fuel line fittings, and inline components are all new. So we now know fuel can be successfully drawn from tank and pumped to carbs, yet still the fuel line is losing pressure.

Within any tube, with any fluid or gas, a pressure can be measured and that value be sustained during application. If pressure is lost/gained in the tube, with all variables remaining the same as when pressure was sustained, you've got 1 or more factors causing the pressure loss/gain:

1. mechanical pump failure = loss of pressure
2. impedance of flow = increase of pressure
3. compromised tube = loss of pressure

It's not #1 or #2 that's causing air to be pulled into the fuel system. Only left with one probability. Do the vacuum test as rodbolt suggested, or pressurize the fuel line as townsend suggested.

Another suggestion is to get your hands on a locking tubing clamp, one that completely crimps down 100% occlusion. Remove the fuel inlet hose from the fuel pump,. Make sure fuel filter assembly is closed tight. Holding the fuel pump inlet hose (fuel filter outlet hose) over a disposal can, squeeze primer bulb to clear all air from line. Squeeze it a bunch, get a liter or so out. Make sure fuel filter canister is higher than tank, AND have the fuel filter outlet port pointing straight upwards to aid in evacuating air from canister. Once air in fuel filter canister is evacuated, clamp the outlet hose.

Now, for the most part, you have a air evacuated tube from primer bulb forward. Squeeze primer bulb until that SOB gets rock hard, hell squeeze it until you can't anymore. Your leak is somewhere in between the bulb and the tubing clamp.

By the way, I don't recall seeing the replacement of the fuel filter canister listed. It's possible it or the screw down top is cracked. The threads of canister or top may be damaged enough to prevent a seal.