2007 DF150 stalling when coming off plane

[terrelldspaulding]

I have twin 2007 DF150's on my center console. The port motor (counter rotation) seems to be having an intermittent issue with stalling when I am backing off throttle. Sometimes is stalls and sometimes it does not. The motor runs fine as long as I am on plane or even slow trolling. I also noticed that it shuts off now when I back it into the water off the trailer. It runs if I get RPM's up over idle and then runs fine after it warms up. I had already replaced both primer bulbs with new ones a couple of months ago when I did my annual maintenance and my fuel water separators were clean when I replaced them. I have heard that IAC motor can cause stalling. Could there also be an issue with the VST? Trying to get these motors in shape before vacation. Thanks!

Also - Just realized I have not replaced the high pressure fuel filter this year. No water or trash was present in the low pressure fuel filter/separator canister and I did replace those. Also, I only use marine fuel so no ethanol ever in my tank.

[Moonlighter]

Highly likely that this is nothing to do with the engine - more than likely it is the anti-syphon valve (ASV for short) that is fitted to the takeoff of the fuel tank that the port motor is attached to.

We had the exact same symptoms on a mate’s Seaswirl a few years ago and research pointed the finger at the ASV failing. The problem is that at low revs, the fuel flow volume is not enough to keep the valve open and so it shuts, causing the engine to be starved of fuel. At higher revs the fuel flow is strong enough to force the valve to open, so the engine then runs fine.

The solution is simple. Get rid of the ASV. Its not required on outboard powered boats anyway.

What I did was to access the fuel tank connections, disconnected the fuel hose, then carefully unscrewed the ASV from the tank takeoff fitting. I took it to the workbench and used a steel rod to punch the tiny ball, spring, and seat out of the inside of the ASV, leaving it effectively as an open hose barb fitting. You could of course simply take it off and replace it with a suitable barb fitting. Reconnected everything up.

Problem solved.

[briscoe]

One thing I discovered this year was I did not have the water separator on tightly. I would find that the primer bulb would become soft, especially in the summer. I had changed hoses, bulb and all sort of things to get past the bulb issue. I was having to pump the bulb nearly every time I restarted the motor.
This year when I changed the separator it was only hand tight. Not even real snug. Put on new gave the extra quarter turn and the bulb primer issue completely went away. Most of the time I don't even prime it to start the trip out. I had no idea that was such a butt kicker. I only change my separator every other year.

[terrelldspaulding]

Thanks for the updates, it appears that I was having a low voltage issue due to a bad battery. Was running port motor off 2 batteries and one of the batteries was dropping voltage when I would come off the throttle. I replaced the battery and seems to be solved. I will probably go ahead though and replace the ASV on both pickups since I do not really need them. Thanks again for the recommendations.