Back again with non starting issue--5.7 OMC Cobra---1988

[ab59]

I have been fighting a non starting Problem with my boat. I had thought that i figured it out but it showed it's ugly head again today. All plugs , plug wires , fuel lines and Holly 4010 Carburetor have been replaced with new or rebuilt. I put the boat in the lake this morning and fished for about 4 hrs . I started it with no problems several times . At the end of the day I tried to start it to leave and no start. Wanted to start for a second then just cranking with no success. I opened the dog house and too the air breather off. I walked over and hit the key and noticed that the electric choke did not move the butterfly on the carburetor. Is it supposed to stay open after starting it several times ? I tied a piece of wire to the linkage , pulled the butterfly closed and hit the key and it tried to start. I let the wire go to open the butterfly and the engine started after repeating this procedure a couple of times. I thought at first that a check valve in the fuel line might be the problem since sometimes it starts and sometimes it doesn't . Now I'm not sure where to look or how to go about tracing the problem down to it's root cause. Had problems with the Holley 4010 at first as well so maybe it's there. Don't want to though thousands of dollars at this just to eliminate what might be the problem.
You guys have any ideas ?