OK. First, The Carb Shop does great work. Q-Jet will be ok off road. I run a smaller needle and seat than that on a stock-ish engine like your application. I try to stay around 0.120 or less. The bigger the diameter of the seat, the harder it ir for the float to shut it off and the more crucial fuel pressure is. 4 psi would be ok, a little low, but you need to check it. If it spikes to 8 or 9 with that inlet, you will have issues. I shoot for 6.5 to 7. The nitrophyl float is good. If it is a late-model, most people take the fuel baffles and well plugs (if it had them) out. I leave them in most of the time to help with fuel control. If (?) you take the top off, look at the primary metering rods. They are on a piston and may be stuck up. That piston needs to move freely. Make sure the top gasket doesnt interfere - at all. Obviously, make sure the choke and all its linkage is working well.