I have a 92 Sea Ray with a Mercruiser 4.3 V6 with Thunderbolt ignition. The problem that I am having is when I am going across the water sometimes it seems to knock when I go to throttle up. It could be a sputter but it doesn't seem like a knock or timing issue. It happens mostly when I am throttling up hard or after I back off and throttle up again. It sometimes doesn't do it at all. It starts and idles fine. Can't figure it out.

I have replaced the fuel filter, had the carb rebuilt, distributor looks fine and set the timing. Is there something with the ignition that could be doing this or is it fuel related?

Thanks! Dave