[holmesge]

My 2002 Yamaha 150 HPDI has begun to die on prolonged slow idle.

Runs fine at normal speeds.

After pumping primer bulb a couple times motor starts easily and runs for several minutes but will die again while at idle.

Any ideas where to start troubleshooting ?

Just recently replaced standard filter with a Racor 10 micron filter. It tightened up easily with no leaks.

Any help is appreciated.

[gcboat]

You just answered your own question. The bulb is shot - replace it and all will be good to go.

[rodbolt]

my guess is the primer bulb is good as its working and manually filling the VST bypassing the two low pressure diaphram lift pumps.
my guess would be your low pressure pumps are failing and cannot pump fuel at low speeds.
happens
its why I reccomend replacing lift pumps every 3 years, also clean the VST at least yearly.
carefully test the system for air leaks, can be done with a vacum guage T'd into the lower pump suction line, you should see at least 1/2" HG and no more than 4" at WOT.
you either have a minor airleak someplace or the lift pumps are failing.
by priming with the bulb your simply bypassing the lift pumps and filling the VST mnually, thats why I dont suspect a primer bulb failure.

[holmesge]

Found that the o-ring on the fuel filter inside cowling is leaking .

Plan to replace the o-ring and the plastic nut that holds this assembly in place.

Suspect I may have over tightened / stripped the plastic nut when I changed the filter a few months back.

Hope this solves the problem.

Thanks for the comments.