Perry advises against using muffler pressure with the regulated pump. Just vent the tank to the atmosphere.
I have the same setup (except with the stock muffler) and it took considerable fiddling to get it right but it's worked well since.

Here's the procedure I used to get it right...a little different from the instructions, but it works. I didn't invent it, but don't remember who posted it first.

Run the engine without the pump to get an approximate high-speed needle setting. Now hook up the pump. The setting should now be rich. If it isn't, increase the pump output (by turning the screw IN) until it is.
The mid-range will probably be rich. Run the engine and note the throttle position when it begins to go rich. Stop the engine and adjust the idle screw so the needle is just beginning to enter the jet at this point. I had to turn mine in considerably.
This is your new starting point and all your adjustments should be minor from here.
Good luck!