Greeting all, long time lurker first time poster.

I have a 225 Johnson model #J225TLERK. Beginning of last summer noticed an issue when putting through a no wake zone boat would start off great and after a couple minutes start acting like it's running out of fuel, and would die granted I didn't use the key switch primer to keep it running. Restart and put in gear again and same thing. Run great at high speed just the idling issue. I have replaced the primer bulb trying to fix issue. Also plugs, filter and the like were changed as part of routine maintenance after having the issue. I noticed today that when pumping the primer bulb I hear air or some kind of noise coming from the anti-siphon valve/fuel pickup area. I have noticed this sound before but always thought it was coming from engine, turns out that isn't the case. I think this may be the magic clue needed. Is it possible it's a cracked fuel pickup tube sucking air or am I casting my lure in the grass(i.e. barking up the wrong tree)? Any other things I should check? I think I'm going to get a portable tank and try running on that to isolate engine or fuel tank issue. This is driving me crazy...