Try running a farily concentrated mixture of Seafoam through it.

ok I'll double check and do all you guys have suggested. Thanks for all the ideas guys, just love to get my boat running the way it should!!

Check the anti syphon valve in the fuel tank. I had the same issue with my old Baja. As mentioned before I would replace the fuel line from the tank to separator

I would look in a different direction. Usually if something is clogged or starving for air/fuel the engine will run OK then the RPM's will diminish. You have the opposite problem, it clears out after WOT. I would pull the plugs and see if there is fouling or traces of water from leaky manifolds.

Secondaries not opening? My friend had a similar problem with his SB with vaccum secondaries. The screws holding the link for the butterflys were loose.

This must be contagious...now mine is doing some thing similar....suddenly this afternoon neither engine (Twin 400+ HP Vortec SBC's) would spin over 3200 and previously today I had a few runs into the low 70's at about 5200 RPM. I'm going to follow some of my own advise!!!

Stay tuned...

You're kidding!! Well I made a bit of head way today. I pulled the plugs and re-gapped them today. I revved about 4400 at wot. I have a bit of a miss while puttering. I'm going to get all new plugs wires and cap soon. Double check the gap on the the before install. Then double check my timing and hopefully I'll be laughing!

My anti siphon tank connections are original as far as I know and being 35 years old and every thing else in the fuel/ignition system being new...that's the first place I'm looking. Cheap $15 part times 2...hell of it is I have to almost take the a$$ end of my cockpit apart to get to them. The devil is in the details for sure!!

did either of you come up with a reason for weirdness?

I just pulled and re-gapped my plugs. Runs like a top now. The gap was small so we figured not a long enough spark so it was loading up on fuel. Still has a slight miss at idle. New plugs wires rotor and cap in the spring should solve that.