Need expert help

[giacomin]

Sorry to be so long winded but you all need to know the backround. Repowered a 22 Proline Walk from a Mercury 200 Carbed to a Yamaha 225 OX66. 2002 power head - rest of motor 1999. New digital guages, previously used motor control harness, oil tank wiring. New throttle, Ignition switch and control cables. Motor runs perfectly - 5500 Rpm WOT. Motor runs perfectly for hours then just stops. Once - primer bulb seemed collapsed. Replaced all the fuel line from the tank to the motor. No anti-siphon valve. Replaced primer bulb with Yamaha bulb. Checked the vent with high pressure air - perfect. Had a Northstar fuel flow meter. Thought maybe the sender restricted too much for an EFI engine. Bypassed it. Replaced 10 micron Yamaha filter. Replaced VST filter as well as the engine filter and the engine check valve. Fuel is perfect and run with Yamaha ring free and Star-tron.
The motor just stops with no warning. The bulb seems relatively MT but the motor starts right up. It may not stop for another hour or another 10 minutes. No warning - no stumbling - just stops. Calm water or rough water does not seem to make a difference.
Any thoughts about the low pressure fuel pumps? I am completely out of ideas. Could this be electrical? I'm stumped! Thanks for any help.

[99yam40]

Monitor fuel pressures and vacuum to make sure supply is good and fuel pumps working properly

Monitor electric fuel pump volts/amps to see if it pulls too much and is shutting off

[jb123]

runs perfect
when it drops out check motor filter level
x2 monitor rail pressure

[giacomin]

JB - will the high pressure pump just quit if the voltage is too high. My main problem is that this occurs out of the blue. I really cannot chance dousing my motor in salt water waiting for it to cut out. I am leaning toward a bad ground or faulty connection. Is there any possiblity that a low pressure pump has a pin hole. I'm thinking that the motor would sputter and not just stop cold. I'm struggling with this one. Thanks for any further advice.

[THerbert]

check Ground cables at battery and motor. Had a loose ground cable at the motor and died while running on plane. Would not restart, but starter would click some times.

[giacomin]

Problem solved

Turned out that the fuel pick up in the tank was almost touching the bottom of the tank. Through years in service - the threads on the elbow were slowly stripping causing the previous owner to continually tighten the elbow. It eventually began to bottom the tube and caused a fuel restriction. Cut 1/2" off the tube - no problem. In 40 years of boating I would not have believed this but having run out of ideas it was the only one left. Problem solved.

[99yam40]

monitoring the fuel pressure/vacuum would have showed that very quickly