92 Sunsport 351 engine running rough

[Thor]

I recently purchased the boat last year and have been doing some general maintenance to the boat. About the 5th time out this year the engine started to pulse while at and idle. Blah... blah, blah.. blah...(sound effect) instead of being at a steady rpm it jumps about 200-300 rpm ever second or so. Any advice on what the issue could be? Or where to start testing?
New plugs
New wires
New coil
New solenoid
New bilge
Fresh oil
New impeller
New packing on drive shaft
New fuel water separator
New electronic choke
New secondary battery

[Salty87]

Have you replaced distributor cap, points, etc?...or is it electronic ignition?

[Thor]

Electronic ignition. I’m starting to think it’s a possible vacume leak in a gasket on the intake side. I’m going to try and chase it down this coming weekend.

[Jetlink]

Does it start up fine cold and then start running like a turd after getting warm? Also, confirm it does not have the Pro-Tec ignition on it as well please.

[Thor]

It’s the opposite. It starts up pulsing rpms. Once very hot, it idles normal. I’ll have to check but I believe it’s prestolite