C115 2 Stroke is starved of fuel after primer bulb flattens

[Soundear]

I have a 1998 C115 TLRW Yamaha 2 Stroke that has been an excellent, dependable motor until recently. After replacing fuel line, primer bulb (2x), water separator, anti siphon valve on tank, pickup tube w/ inlet screen and checking tank vent is clear, it's an absolute mystery as to why the primer bulb is drawn flat. At first, I prime the engine prior to start by squeezing the bulb until firm; the motor starts and runs excellent. 10 minutes later the motor starts to run rough at idle, stalls when shifting into gear, and soon after stalling a few times will not start as primer bulb is flat or very soft. This happens @ low speeds and high speeds. High speed is limited to 30 seconds @ about 4000rpm before temperature alarm in 703 remote sounds. Replaced complete water pump assembly, changed thermostats and poppet valve. (I only mention this separate temperature issue not knowing if there's a connection between overheating and the fuel supply problem) The fuel is supplied from a 27 gallon plastic tank built into the hull that I drained, cleaned, and pressure tested for 10 minutes to rule out leaks causing water intrusion into gas which has the potential to clog the water separator which can possibly lead to gas flow restriction. I still end up with a flat primer! Am I overlooking anything? Suggestions?

 

[boscoe]

A primer ball going flat is an indication that something upstream from the ball is causing a restriction.

I bet if you were to get a new portable on deck tank and plumb it to the primer ball it will not go flat.

 

[Soundear]

Yea, I appreciate the suggestion from someone with your experience. It makes sense; it does trap the problem at the built in tank if the portable tank proves to not flatten the primer bulb. I'm 99% sure the problem is upstream, but with all of the items from the bulb to the tank I checked and/or replaced, why? I guess I'll work backwards and find the culprit......Thanks again!