Mercruiser 3.0 Alpha One turns over but won't start

by Rex
(Conroe, TX)

I just acquired a 1994 Bayliner Capri 1750 with a Mercruiser 3.o Alpha One that had been sitting for three months from a buddy. Got it home and noticed that the battery was dead. Bought a new battery, put ears on it, and fired right up. Went through forward, reverse, and neutral and everything ran fine. Loaded everyone up, went to the lake, unloaded it and I could not get it to start for anything. After about an hour, I decided to load it up and head home. Bought everything for a tune-up hoping that it would solve my issues. Changed the gear oil, plugs, wires, fuel filter, distributor cap and rotor. Placed the ears on it and it fired right up and ran like a top. Loaded everyone up, went down to the lake again, unloaded it, and again it would not start. This is my first ever inboard/outboard and know nothing about these boats or motors. I am pretty well mechanically inclined but without any guidance, I am stumped and do not want to keep throwing money at it with no sort of direction. The plugs and wires were definitely old and needed replaced and I always like to start things off with a fresh tune-up so I know where it stands. This issue doesn't make much sense to me at all and I would greatly appreciate, and accept, all/any advice before I take it to a mechanic. Thank you and I hope y'all have a wonderful day!