I have had the power piston stuck all the way down on 2 of my Carbs over the years, and when it's stuck all the way down the motor in the least misses and may also back fire as both of mine did when you applied the throttle at a certain rate. One thing that's for sure, is if that's the stock power piston spring in there, and seing as you are running a bigger Cam I can assure you that you vacuum level at idle is not enough now to pull that piston down all the way to get the metering Rods in there needed idle position and the motor will be running fat. You likely need a lighter spring once you free up the stuck power piston issue.
The cam is really not much more than a stock Stage 1 cam and the idles at 750 or a bit less and at idle vacuum is 16 hg.
