Possible Trouble Shoot Idea
I had the exact same problem with my 88 Spl. When you have it out and it is acting up, take a screw driver and tap on the power pack and see if the engine reacts every time you tap it. I did this to mine while it was under a load and every time I tapped the pack the engine would respond. I changed the power pack and was out fishing in no time.
I hope this helps