2018 250 Pro XS losing prime idling

[TAH]

2018 Mercury 250 Pro XS #2B526067. Motor has 60 hours. This is my 10th motor in 15 years and have never experienced this. When idling around 3-4 mph the motor dies. Bulb is completely flat. Pump it 12 times idle some more and it dies again. Did this 7 times when fishing yesterday. I just had it to the dealer and they say there is nothing they can do, everything Checks out. March through May motor never ran out of fuel, since May
I have had the issue. One thing I have noticed, up till may when you popped the fuel cap the tank vented hard now it barely vents if at all. Any suggestions?

[lmoore]

I would suggest getting Merc involved. No reason for a shop to tell you there is nothing they can do about a boat under warranty that won’t idle without dying and I can’t imagine Mercury would be real happy to know they have certified dealers out there giving that kind of “service.”

[TAH]

Dealer ran motor in test tank for a hour and it never died.

[Savage]

If the boat is new also,then I would inspect the Fuel Demand Valve.

[TAH]

How is that inspected. New 2018 Ranger Z520L

[Savage]

Your Dealer should know how to test and inspect the FDV.

[TAH]

Thanks Savage.

[Landar]

My new boat and 250 Pro XS is doing the same thing. Did you ever find out what was causing this?

[DR. DROP]

I got a 2017 Pro XS.. On a long idle mine did the same thing when I first got it.
They rebuilt (changed out the check valves in the pulse pump) and have never had another problem.

[EuropeanAM]

Sounds like you either have a supply restriction OR a weak pulse pump. These can easily be tested and confirmed with a Vacuum Gauge installed right at the engine (monitoring the vacuum across the RPM range, which should never exceed 3" hg, on this system).

Can also monitor pulse pump CAPABILITY with the same setup (by forcing a restriction on the supply side of the gauge). This is where a weak pump will show up.