Did you read the tuning instructions from the Factory Pipe website?
Here There's some other instructions I used, can't find them...though they are on the FP website.
I'm running a similar setup to you, I started with the top two screws closed, and opened the bottom up by one full turn. Make sure you are tuning after the carb is dialed in really well. Think I'm running 1 1/8 turn on the bottom screw now, maybe a 1/4 on top screw though can't remember and too lazy to go check. I'm also tuning at 5000 feet elevation, so might have to compensate for that.
My settings are giving me the most reliable across the power band and not bogging down anywhere. Have great top speed, and hits well on bottom end despite having a very over pitched impeller. I'm running a 44SBN, Factory Pipe, High Comp Head, and a 14/19 SOLAS.
Though yea, I found when I retuned my system after rebuilding a few weeks ago, once the carb is dialed in really well, start with 1 turn open on bottom screw and adjust from there. Once it feels the pipe good, play with the carb and pipe for the really fine tuning.