How do I safely remove anti-siphon and intake line?

Very interesting thought. This is one possible reason my boat won’t start. I have always winterized the fuel with Marine STABIL. I put in fresh 87 octane which can be up to E15 ethanol here. The fuel is definitely a year old. I suppose I could just draw some of it out and see if it burns in something else as a quick and dirty test. I think I will try this since it’s easy to do. Thank you.

I would not use E15 in any marine engine, in fact marine engine companies have said this. Also I'd use higher than 87 octane, use at least 89. The problem with E gas in general is that the ethanol absorbs moisture in the air and especially on older boats with open fuel tank vents, it can lead to the water and ethanol separating out from the fuel leaving water in the bottom of the tank with the ethanol and the rest of the tank will have low octane gas that doesn't burn well in a marine engine. After my problem last year I had the tank pumped out by a guy that does this for all the marinas around here and filled it with 30 gallons of 94 octane Sunoco straight gas. I ran this gas in the outboard tank test I did last September and the boat ran great on it. There are only 2 gas stations in all of Long Island NY that I know of that sell straight gas with no ethanol. All the gas docks sell E10 fuels. In the future I may just have whatever is left in the tank drained a the end of the season to avoid a recurrence. Now I used E fuels for at least 15 years and didn't have this problem, but it wasted a lot of time for me because I didn't think of the fuel as the problem.

Have you removed the fuel filter and dumped out the contents into a clear jar? Let it sit for a day or 2 and see what it looks like. If you see a layer of water on the bottom, that's phase separation.

Just updating the thread since it’s been awhile. I’m finally back at the boat. I got the square head to turn thanks to advice with PB Blaster. I pulled out the tube and the screen on the end actually looks great. I’ll replace it all since it’s out, along with a new anti-siphon valve. Now that I have visually inspected them however, I don’t think this is my issue. I’m thinking right now that advice on the fuel itself is problematic, or, my Cool Fuel pump is the issue. The water separator filter is new as well. Happy to hear any other advice also.

Summary:
-no pressure reading from the valve with a gauge
-anti-siphon and line in tank appear to be clean and good
-water separator filter is new and filled with fuel

Good work trying to leave no stone unturned.
I’d get an outboard tank and run it with fresh gas if it runs good that will tell you if it’s the fuel in your main tank. Don’t know anything about the cool fuel module so can’t say it it’s also involved….