I am the proud owner of a '78 Catlina express cruiser. I inherited the boat from my deceased father-in law and have been restoring/cruising for the past 6 years. As an auto shop owner of 30+ years, I have a little bit of mechanical comprehension. The engine was replaced last year and upgraded to the 350, we also added electronic ignition. We can now cruise at 3200, 25 mph, at 8.2 GPH! The problem we have is after cruising a while (warmed up), and then idling for 5 minutes or so (like in a no-wake zone) and then re-applying throttle, I get a very extreme surging from a near stall up to 3000 rpm, the cycle from near stall to rev-up is about 1.5-2 seconds, and it will surge for about a minute, decrease in intensity, and then go on down the bay like normal. This condition was prevalent with the old engine as well (we've had this symptom for the past 3 seasons. I can't be sure, but I believe after 1 of the exhaust manifolds was replaced the symptom surfaced. I suspect maybe the fuel filter (bolted to the front of the starboard exhaust manifold) or the fuel line may be heating up and vapor locking. I'm hoping one of you kind souls has seen this before and can help get my pointed head facing the right direction !!