250 hpdi falling off...

[87gtNOS]

This motor has all filters, including mystery done...runs perfect.
Today tromped on it, 5400 rpm I felt it drop off, like ignition...let off, pulled up to friend's dock...quick top cylinder plug check, plugs perfect.
Pull out it ran fine, went 1/2 mile to next fishing spot and after fishing, pulled out it struggled to break 3000 rpm or so...I stayed in it and got it plained and cruised fine at 4700. Later on, I tromped on it, did it again, so I feathered the gas and stayed in it at 4000 rpm or so. Cruised at 4700 or so the rest of the way home, 45 mins.
Compression check all cylinders perfect. All plugs nice. Drained some of the vst, no water.

Ideas?

[87gtNOS]

Idled perfectly each time...

[yam911]

Need to be monitoring high pressure pump output when it starts to fall off.

[87gtNOS]

Oh. Could voltage affect this?
Last time out, stereo on, it did died slightly, I switched stereo to starting battery only, as I had the stereo on 1 and 2 (yes, stereo is on batt selector switch!). #2 battery is one of trolling motor batteries. So it was run down somewhat, so my thinking was it was struggling to charge it. When switched to both, the motor showed 12.4v....when I put it back to #1 it was 12.9 or 13. Didn't hesistate again that day.

[87gtNOS]

Need to be monitoring high pressure pump output when it starts to fall off.

The drop off is instant, like letting off the gas...perhaps a surge

[87gtNOS]

Primer bulb...won't get hard.
. I just put a new spare I had on it and it pumps up better.
Then changed filter on side of engine with the water sensor. My sensor float might have been stuck up all the way. But no water in that fuel.
Pushed it down, slid new filter up onto housing and then threaded cup on (old filter one was a yr old and clean).
Primed primer bulb and it goes hard now....

[87gtNOS]

Went back out to find replacement primer bulb also staying sucked squished...no restrictions found before the bulb.
New YAMAHA bulb to be installed tonight.

[87gtNOS]

Here is my bulb on the left with an old merc bulb on right, merc bulb sucking on left bulb...left bulb staying squashed.

[87gtNOS]

nope...not primer bulb.
Checked plug boots, ok.
Changing VST filter tonight....new plugs too...even though old plugs looked perfect...

[87gtNOS]

NEW VST FILTER, no luck...

Link and Sync and I THINK it has cured the problem, cruised at 5000 rpm for a good 30 minutes, with 70+ mph spurts and no dropping off. I might have felt a drop off once, but that could have been a wave at 65 mph.....
0.62v on the TPS once the throttle plates have been set at 0.51v closed seems to give a little high idle...900rpm ish....

fingers crossed.....