Let's be more specific on how full your seperator is.

The threaded nipple is the out of the filter/seperator which goes to the IN of your fuel pump. If the fuel level get's just below this, then your pump won't pick up fuel.

So, if seperator seems full, it may actually not be full enough.

Think of this threaded nipple exactly the same as the fuel pickup in your tank.

Maybe the attitude of the boat at cruising speed along with higher fuel demand is when it starts lifting water off the tank bottom. Also when you pull the pickup tube take a good look at the hose to your pump.

Maybe someone put a ping pong ball down your filler ? LOL.

Any old people like me remember the ping pong ball in the tank stories that ran around like wildfire ?
Tons of people I knew at the time said they've done it to others but I never saw any evidence supporting they where telling the truth. LOL.

When I spin the filter off the center part appears to be 1/2 to 3/4 full while the outside ring where the little holes are seems to be all the way to the top. I will have to pull when I get home, but I honestly remember the filter looking like this when I pull it off. I dump everything out and then spin it back on with nothing in it and the motor will fire right up and fuel pressure will climb from 0 to 6 psi in about 5 seconds.

I remember the marbles in ensign pulver, lol

Does the fuel psi gauge show vacuum by any chance ?

I've not read this whole thread but It doesn't sound like the fuel system is breathing, by pulling the filter your breaking the suction, try loosening the the fuel fill cap when it dies and see if it will refire, just a thought

The gauge shows no vacum only the fuel PSI. Next time it drops down to an idle and shows 0 psi i will open the filler and see if the pressure pops back up. I feel the tank is venting ok because when I fill up at the pump and I feel the air rushing out at the vent. Could anything else besides a clogged vent cause vacum?

Collapsed line or antisiphon valve closing. When you crack the filter the line can reopen and same for antiphon valve.

Or, a ping pong ball in your tank closing off your fuel pick up. LOL.
Edit in: debris like a plastic bag / decal/ or etc could do it too. I had a MG here that did this and I finally pulled tank and found hunks of cork in it. I guess MG's used cork for the floats on their fuel level senders.

Fill a straw up with water, put thumb over one end. Trying sucking the water out of the straw.

All lines are 2 years old so I dont think they are collapsed anywhere, however, I will go over them all again tonight. There is no check valve at the tank anymore. It was removed 5 years ago. Unless someone hates me I doubt there is a ping pong ball.

Maybe a fishing bobber ? Any kids that like stuffing things into empty holes / slots ? LOL.

I agree with above - for schits and giggles to truly check the venting - take off gas cap instead of cracking seperator.

I will do that if it happens this weekend when out. I am curious to see what is in the tank when I pump several gallons out tonight. I am leaning more and more towards this being a water issue than anything else, but I could be completely wrong. Historically I have hooked a hose to the pickup and pumped that way but I am going to remove the pickup and put a hose into the tank with an aluminum welding rod to make sure I am all the way to the bottom part of the tank.

Sounds like you have a lot of sediment in your tank. If it's salt or aluminum oxidation, it's almost invisible.When you shut it down ,the sediment drops away from the filter element. Emptying the filter will get the water out but you still have crap in the filter. Sediment in tanks mix much better w/todays fuels.When I drain filters into clear containers (even fuel claiming to be ethanol free from our local fuel dock),it takes much longer for the water and b/s to settle out. Drain tank and couple of fuel filter CHANGES ,not just draining filter,hopefully will get it. Good Luck!

Here are tonights results after some wrenching:

I) Filter pulled and dumped with no signs of water.
II) 5 gallons from tank pumped out with less than a half a shot glass of water collected after an hour of sitting.
III) Fuel lines all solid with no signs of collapses and all fittings tight.
IV) Fuel line moved away from water circulating pump to avoid heat realted issues.
and for the only issue.....
V) Pickup pulled from tank and the pipe was loose from the fitting. I tried with my mouth blowing into it with the end plugged and didnt feel a leak but I would have to assume with it cracked all the way around and wobbling there must be a leak. I am not convinced this is the problem because why would the engine fire right back up and run ok for awhile?

Any thoughts would be apprecited before heading back out this weekend.

Thanks again.

Jed

Can you take a pic of your pick up and fitting and post here ? I'd like to see this 'crack.'

I'm curious if this problem started at the same time you replaced all the fuel lines 2 years ago?

I will try and post a pic, however, the fitting is a 90 degree which threads into the top of the tank and then a pipe (looks to be copper) is braised to the 90 degree fitting. The whole braised bead is cracked and the pipe wobbles inside the fitting. I took the other pickup from the port side which was solid and used it as a replacement.

I don't believe this is from when the lines were all changed because the only piece from the pickup replaced was the anti-siphon which is threaded on the opposite end of the 90 degree tank fitting which has never been removed before.

Would this wobble in the pickup cause a drop in fuel pressure over time?

I believe the cracked pickup was the issue. I have been out several weekends on the same fuel water seporator and the new fuel pickup with no issues (knock on wood) at all. The boat ran flawlessly with no hint of ever wanting the shut down. The only other thing which was done was moving the fuel line away from the water hose. This too might have been the issue, however, this hose has been like that since I had the boat when it had no shut down issues.

Thanks everyone for the help.

The best thing to do trying to find fuel issues is separate your fuel tank side from the motor side, Take the boats fuel tank, fuel itself, valves, fittings, anti siphon valve, fuel pick ups and the fuel vent completely out of the mix for testing purposes.

Unhook your fuel line coming out of the boats fuel tank at the first fuel inlet on the motor side and hook a portable gas tank with fresh gas, good quality fuel line and a good quality outboard primer bulb. head to the water to run the heck out of your boat, If motor runs great - you found your problem to be NOT the MOTOR SIDE. Its that simple. Been doing this form of testing for 35 years and running. Saves time and saves money as well along with locating your possible problem area..