take off the PMI reg. you dont need it, your just going to starve your valve of air. If you get a barrel leak, it usually means you need to go down a carrier. As Orge said, you need to use the same o'ring when you do this. Just try the 1.5 carrier with 2 shims and the long spring with that same o'ring(without the PMI reg). Before you gas up, back your velocity out so it doesnt fire, then slowly turn it up bit by bit till the marker fires reliably. Tell us how it goes.
what type of valve and settings?