The whole point of the powervalves are to give you adjustment in the midrange circuit.Cater,Edelbrock and Quadrajets accomplish this with stepped metering rods,which you probably already know.Since Holley doesn't have anything restricting their jets,they use the PV's to do this.All carbs have and idle,cruse and WOT circuit.The PV is the cruise circuit so to speak.If your car is in need of extra fuel(undr load) tha manifold vacuum will drop,allowing the spring pressure to vercoma the vacuum and allow extra fuel in.If you plug the PV off,you have to compensate by jetting up alltogether,which is usually a waste of fuel.A race only car only needs to idle and run WOT,so you chuck the PV 'cause you don't really need it,and to remove something that could fail,IMO.So,the real disadvantage is burning extra fuel,but it can also cause drivability problems.As far as the acc pump shot,if it is out of tune,it will act up immediately when you stomp it by over-fueling the motor or leaning out.Over-fueling will usually act like a stumble/flat spot and leaning out will usually stutter and pop.Feels kinda like a set of points that are sticking.I don't know which cvam is on your pump shot,but usually it takes a real touchy car to have problems out of that.I mean,you can sometimes find definite improvements there,but usually doesn't cause major drivability issues.I would start with size 31 squirters front and rear.That seems to have worked on just about everything I have ever tuned.If you think that your pump shot is "running out" too soon,use a cam with a longer ramp.Look for a longer one,not a taller ramp.Also,for a street driven car that hits bumps and potholes and such,a pump shot that is adjusted woth no lash will dribble a little fuel every time it gets shook.I like to put a little bit of slack in mine,not much,just enough so that it's not tight.A 4-speed car,though,will just about need the pump shot to come on instantly,since a clutch will put more af a strain on the engine than a torque converter will.This might sound dumb,but if your flat spot is primary only,it might just be lean.What jets are you running front and rear?It's best not to stagger them more than 2 jet sizes.If you remove the powervalve,you will have to jet up 5-10 sizes,depending on the car.I don't know if I answered any of your question,but my fingers are sore from all this rambling.Talk to you later
