I have a QF Slayer 750 Vac Sec and I have battled that thing since day one. Very rich at idle, mixture screws are only turned out maybe 1/4 turn. I have tried air bleeds, adjusting secondary throttle plates, checked and rechecked transfer slot and I can not get that thing from being very very rich. Power Valve good, tried different IFR's, the list goes on, lol. Right now I have it all back to stock settings and I am trying to go at it one more time. Even getting the secondary opening dialed in has been a pain. It supposed to be easier with their screw adjustment but I haven't found that sweet spot yet. I can not figure out why that thing keeps dumping so much fuel at idle. Good luck to you and I am curious to find out what works for you. That Holley 650 VS sounds interesting. I may look into that or possibly bite the bullet and give the Sniper a try.