96 GTI 3/4 - Full Throttle dying

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Earlier this year I rebuilt a 1996 gti. I replaced all the grey fuel lines with mpi marine grade fuel injection lines, completely rebuilt both carbs with parts from osdmarine, rebuilt the fuel baffle (float sensor was not floating), replaced fuel selector, replaced fuel pressure check valve, and all filters inline (both in fuel separator and carbs).

I've had the ski running flawlessly for a few months now. My carb tuning is pretty much identical to the book. I believe i went with a 1/8 turn deviation to lean each carb on the low speed screw side of things. A few days ago I was gunning it across the lake and felt the engine just die. I let off the throttle a bit and the engine came back. At that point I just let the engine idle for a minute or two, testing short bursts of throttle for a few seconds each. I slowly punched the throttle to 1/2 and just kept climbing to find the problem location. Somewhere around 3/4 to full throttle it happened again. Engine ran fine at that position for a few seconds, maybe 5-7 seconds, then just tried to die. I kept trying this over and over trying to figure out what it might be, never letting the engine die. I would sometimes decrease throttle and keep going or just return to idle. I was pretty far from the location I launched from, but was able to get back there without the engine dying (took me about 30 minutes).

I figured it might be spark plugs fouling, so i cleaned them with gas and a propane torch. Was able to get them clean that night, so I took the ski out the next day. Same issues as before. I was able to leisurely stroll around the lake for an hour or 2. Just couldn't go full throttle for more than 5 or so seconds without the engine trying to die.

I had an issue previously where I had a leak in the exhaust pipe that caused a spray that was getting sucked in by the carb months ago. I hooked the ski up to the hose yesterday and started it to verify this wasn't the case.

At this point I figure the issue is that I'm not getting enough fuel to the carbs at full throttle. I imagine what is happening is I am sucking air somewhere, and its most pronounced at full throttle. I've ordered part #17 from the fuel system diagram, as I remember reading that the fuel separator is one of the common areas where air might be getting in. Now that I think about it, I never replaced this o ring when rebuilding the fuel system. When i unscrewed the fuel separator bowl I did see some particulate at the bottom of the bowl.

Any idea what could be causing this?
I did break apart the carbs to check internal filters and jets. None of the jets were clogged and none of the filters were clogged. I was able to spritz brake cleaner through the carb jets.

I may try and bypass the fuel selector and replace the oring for the fuel separator the next time I go out on the ski. Other than that I guess I'm performing a pressure test of the fuel lines. I can't really think of anything else it could be.
I put in a new fuel separator oring and the ski ran fine for a day. Took the ski out again today and the issue reappeared.

Every time this has happened I've had less than 1/2 tank of gas. I'm gonna fill completely up and see if the issue disappears before I pressure test the fuel lines.

I must have filled up enough after adding the oring in the fuel separator, that the issue disappeared earlier last week. I filled up completely and drove the ski all over the lake back down to 1/2 tank without issues.

It appears that the ski has problems getting fuel out of the tank once the fuel level drops past 1/2.

I'll try running the ski on reserve my next time out to make sure that less than half a tank is still usable. I'm sure there are some aftermarket fuel pump options out there to mitigate this.
Just run the reserve line directly to the carb(s) bypassing the fuel selector and water separator. If it runs good then you know the issue is one of those two. If not, then its likely a carb issue or air leak.
I took the ski out a final time to check the fuel selector. This time I ran on reserve and was able to drain the tank indicator on the gauge down to empty running it full throttle without issues.

I imagine the baffle just has issue picking up gas when the fuel gets too low and the reserve setting isn't being used. Guess I'll just add gas when this happens
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