Need your thoughts please

Last week end i started all my engines one after the other to change oil. First started right up but died after 30 second, but ran fine before that. Tried to restart a couple time and did not work . When to do the same with the 2 other and evrything went fine, did oil change and water separator change.

Fuel tank was low but not enough to run out of gas in my opinion since everything ran fine the last ride of the season. Did not take a chance, filled fuel tank last thursday.

Tried again that dying motor yesterday. Started right up again, ran for 30 seconds and died again. Would not start again after that.Took off the water separator, it was 2/3 or 3/4 full, so i filled it and put it back on, started right up for 20 seconds, died and wont start again...

Whats your guess? Varnish from winter in the injector or somewhere else? Bad fuel pump? Clogged fuel line? Should i blow the fuel line backward from the hose at the water separator? Or? Or? Or?

Thanks

Check the gas tank vent line too. If blocked from spiders etc.

Easy test for vent, loosen or remove gas cap and try starting. Maybe weak low pressure pump. Can you put a Guage on it?

EFI motor- can you check for trouble codes? Something telling ECM to shutdown?

Pull a plug wire to see if its fuel or ignition when it shuts down. If it ran when u put it away chances are its fuel related not ecu electronic. Was it in heated storage? Premium fuel in it or not?

When you try to start it the second time, can you here the high pressure pump cycle ??

all good points to check will try those next w end! i dont have a computer to read the codes so will try all suggestions you guys gave!
premium fuel in the boat, was not in heated stroage, yes i can hear the fuel pump priming at least the noise is there! not sure if it primes!
more to come! ran out of time last w end to work on that!
thanks again!

I would recommend trying to get a remote test harness and a remote fuel tank. This way you can isolate the engine from the boat. You can make sure it's not a fuel supply issue as well as make sure there isn't something electrical on the boat causing a problem

IAC sensor

I just had this exact problem on my 525. Turned out to be filters. BOTH water separator and fuel rail. They were both changed just last November before a race.I didn't think there was any way they could be bad in such a short time. I also changed the mechanical fuel pump on top of the water pump as a another thought.