OX66 Fuel Supply Troubleshooting HELP request VMAX225

[JimmyTilt]

I don’t understand what is happening. Engine runs well for long durations. After Stopping for 10+ minutes, fuel lines drain back to fuel tanks of my 2002 Skeeter ZX225 and engine stalls on restart after fuel in VST is expended. I have to reprime with bulb every time I turn off the engine after it sits for 10 mins or more (10+ pumps of primer bulb until hard). Engine then runs boat well on plane thereafter. Boat Setup is two fuel tanks to tank selector switch to primer bulb (with enclosed back flow preventer) to 10 micron fuel/water separator to cowling filter then through Yamaha fuel line back flow preventer to 3 parallel low pressure diaphragm pumps to VST.... I replaced almost everything and problem persists. New primer bulb mounted vertically (replaced twice, now with Quicksilver brand) new Yamaha fuel line back flow preventer, 3 new (generic) low pressure diaphragm pumps, crimp clamps on all fuel line fittings in bilge, and 2 new gas filler caps (black plastic with overflow return) installed during restoration. There are no visual fuel leaks detected. One other clue is that after priming, there is not enough system suction at idle (800 RPMs) to maintain fuel lift from fuel tanks when fuel levels are low in fuel tanks causing engine to stall after 5 minutes or so of idling. As RPMs (and vacuum) increase, engine runs normally. I am not sure how fuel can drain back through the primer bulb, but it does. There might be a pinhole leak in the fuel line system somewhere to break the suction, but I can’t find it. Anyone have any ideas?

[bpicinc]

About the only thing left is the Yamaha fuel line back flow preventer.

[yam911]

I don’t understand what is happening. Engine runs well for long durations. After Stopping for 10+ minutes, fuel lines drain back to fuel tanks of my 2002 Skeeter ZX225 and engine stalls on restart after fuel in VST is expended. I have to reprime with bulb every time I turn off the engine after it sits for 10 mins or more (10+ pumps of primer bulb until hard). Engine then runs boat well on plane thereafter. Boat Setup is two fuel tanks to tank selector switch to primer bulb (with enclosed back flow preventer) to 10 micron fuel/water separator to cowling filter then through Yamaha fuel line back flow preventer to 3 parallel low pressure diaphragm pumps to VST.... I replaced almost everything and problem persists. New primer bulb mounted vertically (replaced twice, now with Quicksilver brand) new Yamaha fuel line back flow preventer, 3 new (generic) low pressure diaphragm pumps, crimp clamps on all fuel line fittings in bilge, and 2 new gas filler caps (black plastic with overflow return) installed during restoration. There are no visual fuel leaks detected. One other clue is that after priming, there is not enough system suction at idle (800 RPMs) to maintain fuel lift from fuel tanks when fuel levels are low in fuel tanks causing engine to stall after 5 minutes or so of idling. As RPMs (and vacuum) increase, engine runs normally. I am not sure how fuel can drain back through the primer bulb, but it does. There might be a pinhole leak in the fuel line system somewhere to break the suction, but I can’t find it. Anyone have any ideas?

When the motor is turned off the VST should be mostly filled. When the motor starts it should be able to run on the VST supply long enough for the lift pumps to start keeping the VST filled.

Assuming there is no adverse restriction in the fuel system supply, the pumps may not be doing their job.

Have you plumbed a vacuum gauge into the system to see what is going on? Use of clear hose will allow you to see any air bubbles from leaks.

[yam911]

What is this back flow preventer of which you type?

[yam911]

[201pro]

Get rid of the lift pumps and do the electric pump upgrade and you will thank me.
It has been 7 years with no fuel issues since installing the electric pump.

[JimmyTilt]

What is this back flow preventer of which you type?

. Fuel Feed Assembly according to the parts diagram - just a $27 one way valve

[JimmyTilt]

Get rid of the lift pumps and do the electric pump upgrade and you will thank me.
It has been 7 years with no fuel issues since installing the electric pump.

Your suggestion was never on my radar, but makes sense. I will research it. Thanks

[JimmyTilt]

Thanks. Will blow the dust off the mity vac and start that process.