Extreme surge after extended idle '78 Catalina Express Cruiser

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 !!

yes, and the throttle is being applied to the carb exactly as it is when the engine is not surging (not a throttle linkage issue)

she will even give me a lean backfire if I apply too much throttle during these symptoms

we did have these symptoms with the old engine as well

I'm having trouble with a consistent intermittent clog, that goes away, and will come back only after warm and extended idle, then it clears itself out? not some kind of vapor lock or carb icing??

By the by, the fuel pump is new, carb overhauled (remember, same symptoms, 3 seasons) and she will crest 4600, and she can cruise at 3800, just not as economically.

Thanks for the reply.... yes, if I get carb cleaner or brakecleen (alcohol) to the flame arrester, she'll light right up (as long as I enrich) but I really do not think its a clog or restriction in the carb. How does it disappear, gradually over a 1 minute attemp to re-accerate? New news, however, I seem to be missing 2 aluminum spacers between the exhaust log and the fuel filter housing. (I have the old canister filter, new element this season, of course) I think log heat may be boiling my fuel and vapor-locking the filter. I'll let you know, off to make some spacers.........

I Have to tell you Cap< I did not fix my surge (which was even worse this weekend in the 95 degree heat) but I did cruise at 3600, dropped to 6gph and picked up 5mph, I could kiss you. (good thing you're not here)

Ok, I finally fixed my boat (and boy do I feel stupid!) I isolated that fuel filter housing, I insulated the fuel pipes with some heat reflective sleeving from the napa store (and it looks pretty on my new engine) and although I change that remote filter every season, I have not replaced the carb filter. When I rebuilt the carb (as a GM tech I think this would be about my 2000th quadrajet overhaul, one more reason I wasn't buying into missing something) I figured i would go back to the fuel filter without the check valve (I put one in with the check valve to help alleviate the carb drying out after sitting a week-it didn't work anyway) weelll....... after I cut that filter open and found all the dirt packed inside.... well we went for another ride! I guess the dirt would pack itself in after a cruise and really silt into the filter at idlem and well, not flow very well. Whay a dumby. well capt., I guess I can kiss that 6 gal per hour goodbye, but my '78 catalina express 254 sure does run sweet now. Thank you all for putting up with me..