[THEFERMANATOR]

Trying to get a few more details here MJ.

When the problem occurs it is at high RPM's correct?
What happens if you come off plane and run it for a few minutes and then get back on plane?
Does the problem immediately return or does it take a few minutes again? What happens if you go WOT?
How many RPM's is it actually dropping when this happens?

The more I think about your problem, the more it sounds like a restriction going into the float bowl in front of the needle and seat. This would cause it to run good for a minute or 2 until the fuel level in that bowl drops below a certain level. Then it would go to missing. If when you come off plane for a few minutes it comes up and run's normal again I would check for a blockage in one of the carb inlets, or possibly a blockage in front of one of the main jets. To check for a blockage going into the carbs. Drain the bowls out and leave the drain plugs out. Get somebody to pump the primer bulb and look for fuel to come out. You want to look for the drain that doesn't have much fuel coming out of it. If they all drain out the same amount then it could still be a blockage in front of the main jet.

I've seen this happen before on a few occasions where you have a fairly large piece of debris floating around in the carb bowl. It takes sometimes 30 seconds, sometimes 5 minutes for the debris to cover the main jet over. A blockage in the needle and seat entrance will normally take the same amount of time every time for the problem to occur.