2018 Lexington 523 with Suzuki DF 115 that keeps stalling

[Old Yeller Boater]

bought this pontoon new in 2018. lately it has been stalling about every 100 yards. if I run slow RPMs, it takes longer to stall but pretty much same distance if I power up to near full throttle. still stalls. if I use the primer bulb and give it a couple squeezes, the boat will run fine until the next time it stalls.

I checked and replaced the fuel filter. it had a bit of sand/dirt. I am thinking this is a venting problem though. I'm totally unfamiliar with the hose routing and could use some pointers as to where/what to check. I've attached a pic below. the green line goes through the primer bulb and on to the motor. the red line goes back under the boat. as the boat has metal plating underneath, I can't really see where it goes.
could someone suggest how I can troubleshoot this further and get it fixed?

thanks in advance!!!

 

[CaptnKingfisher]

I think you're on the right track about a vent issue. Try cracking open your fuel filler cap and running the boat and seeing if the stalling problem goes away. If so, then you've confirmed your diagnoses

 

[HotTommy]

Try this forum: https://forums.iboats.com/forum/yamaha-suzuki-outboards.28/

 

[Old Yeller Boater]

A bit of additional information as I've been searching through the boat. The red line appears to go under the boat and come up in the storage compartment connected to some type of EPA filter which vents to the exterior of the pontoon.

there are two screw on covers in the rear storage section of the pontoon. removing them, I can see an additional fitting into the gas tank with a line that appears to run from that fitting to the front fitting where the hose marked with red arrows comes out. there appears to be another fitting under one of the screw covers which may be for a main fuel flow to the motor. the line with the primer bulb comes from a different fitting in the fuel tank and I am guessing that's a "bypass" to prime the motor in addition to the main fuel line.

the thing that has me truly scratching my head is where there might be some type of venting problem going on. This is just about as frustrating and chasing electrical problems on motorcycles!