[MarshVR4]

This problem has been present for a while and I've done a few things to try to fix it, but nothing has worked. It seems to be losing fuel at idle. Here's what happens:

I can run all day long at speed with absolutely no problems, it runs perfect. Then when it's time to try to hold position at a rig and keep the engine at 600 rpms for long periods of time, it eventually stalls out. After this happens, I have to prime it for a while before it will start and remain running. If I get it primed good, I can run again at full speed with no problems. I changed the low pressure fuel pumps and just as I was commenting about how I thought it seemed to have fixed it, it died again and took awhile to get primed again.

It seems like there must be either air getting into the system, or the line siphoning itself back to the tank when there is little to no suction (at low engine speed). After running for back in from a trip, or anytime where I haven't sat at idle for a long period, it will start right back up. Anyone had a similar problem? How did you fix it? I really doubt it is a filter problem, because it only happens after long periods of idling. It runs flawlessly at higher speeds.

The boat is a 30' grady white marlin, twin 250s (port motor is problem motor).

I don't have any fuel leaks in the line up to the motor, but could I have an air leak somewhere? Please help.

[ICEMAN]

Try putting a piece of clear hose in the fuel line to the motor, run it at the speed you say it stalls. Watch the hose, if you see air bubbles in the hose, you could have an air leak in the hose, or you could have a bad antisyphon valve, causing a restriction in the fuel line. A fuel vacuum guage, can be put the line and see if you have a restriction. Poor quality fuel can vaporize at 4-5 inches of vacuum. making it look like you have an air leak.

[MarshVR4]

excellent ideas, thanks.

Where is the anti-siphone valve located? At the tank on the fuel delivery line?

[Yamajoe]

Have you tried using a portable fuel tank? If this works, then your problem is somewhere between the filter and the tank.