Air Bubbles in Clear fuel line 150 hp 2002 OX66

[Smily]

I added a clear hose in the fuel line. I installed it just before the engine mounted fuel filter. When The motor is revved up, (increased RPMs), you can see air bubbles coming up the line from the fuel tank.

I did notice that the primer bulb is sucking down, (compressing) as if a great vacuum was sucking it down. Is this a sign that the fuel line is blocked?

I checked for leaks and blockages in fuel line, I cannot find any significant leaks if any at all.
I did remove the check valve or anti-siphon valve from the gas tank as it seems to be the only blockage. It seems to work but it takes a lot of suction to open the valve. I removed it and installed a straight through fitting.
It seems to have corrected the air bubble problem.

I think the motor was trying to draw fuel and the Anti-siphon valve was preventing fuel flow, therefore the vacuum was pulling air from around every hose splice or hose clamp, like the ones at the fuel water seperator , the primer bulb and any other place it could get air with enough suction to pull air in.

Any thoughts on this and how can it effect engine performance?

 

[Smily]

Re: Air Bubbles in Clear fuel line 150 hp 2002 OX66

Anybody? Rodbolt??

 

[rodbolt]

Re: Air Bubbles in Clear fuel line 150 hp 2002 OX66

at the fuel pump inlet system vacum is 4"Hg maximum.
most likly instead of sucking air you were seeing fuel boil.
as vacum increases the boiling point of gasoline drops dramatically.
thats the whole point of a Vapor Seperator.
makes sure the high pressure pump has a clean bubble/vapor free pool of gas to draw from.
excessive vacum will eat lift pumps and create poor running at high speeds.

 

[Smily]

Re: Air Bubbles in Clear fuel line 150 hp 2002 OX66

Thanks, RB.
How is vacuum regulated if it is too high? I was under impression that vacuum is generated by LP pumps.

 

[Smily]

Re: Air Bubbles in Clear fuel line 150 hp 2002 OX66

RB?

And on regulators, can the pressure regulator in the VST go bad and can it effect the performance of the engine?

 

[rodbolt]

Re: Air Bubbles in Clear fuel line 150 hp 2002 OX66

vacum is generated on the suction side of the lift pumps,pressure on the outlet side of them.
generally a good clean water seperator will create about a 1"Hg vacum drop.
a decent anti-siphon maybe 2" but 4 " at the lower lift pump for 200 HP and below is maximum allowed at WOT.

 

[Smily]

Re: Air Bubbles in Clear fuel line 150 hp 2002 OX66

So, how do you regulate it, if it is too high?