I have a couple of questions for you. One being, have you measured the diameter of the bore thru the perry carb? I'm thinking it's still too big for this engine. The bore thru the Magnum carb, with the sleeve installed , is .388. This works very well, but doesn't work without the sleeve.

Secondly, the prop you are using may be too heavy to allow for rapid spool up. My engine did what yours does on an 18-8, but on the 18-6 it was better. When the engine spools slowly, it is sucking in gobs of fuel and not able to burn it fast enough, so it loads up for a while, then clears up. If your engine won't run without tank pressure, I'd say that this still points to the carb being too large. Mine will run without the pressure line connected, even at full throttle. If the engine relies on the tank pressure, it becomes a tuning nightmare because the pressure is not always the same. If the tank pressure is just an aid to the fuel delivery, then it becomes easier to tune.