The secondary can slightly change your RPM's, but is used usually for just fine tuning. I can't remember off the top of my head what was stock in the primary, but you'll need to add some heavier rivets. My sled stock ran, 9100 rpm's. It sounds like yours may have some mileage and could be wearing out your primary spring. Hopefully someone chimes in on what weights you should try.
I don't think I have my notes for clutching for a stock venom, since I switched to triple pipes, but I do remember going up to the next size weight in each hole to bring my rpm's down, and did play with helix's.
I played with a Hauck clutch kit that consisted of 8AB's, stock primary spring (g-g-g?) and a shallower helix from stock that was OK. The 8AB's woke the sled up on the bottom end and pulled nicely. It just petered out quickly towards the top. I wish I had more for ya, and I'll keep looking through my notes.
Drew