I tuned my Q series QFT 750dp with a 9.5 4 window by simply stretching the existing spring. It opens around 12". I run a 69 PJ with .070 PVCR to keep the highway cruise at 14.5 and WOT at 12.5 with a 86 SJ. With a 9.5 PV the car had a slight stumble rolling the throttle with primaries only. I chose to not cover the stumble with more pump shot. The spring stretch cured the stumble (added fuel when I needed it). At the track my AFR is still good when stomping the pedal during launch. If you understand how all the different circuits of a carb work you soon realize that there is more than one way to get it done. I use my car as street/strip and this works for me.