Needle seat hole diameter if small would just be at high power levels and speed. So which do you recommend ? So are you saying a too large hole would just splash in too much fuel and cause a rich condition?
Yes, I am. Too large of an orifice is maybe like comparing a garden hose to the little tube in your toilet bowl that irrigates the overflow tube. It will allow more volume and that volume may be too much for your float & needle to handle correctly...even if your fuel pump pressure is okay. If you're pushing too much fuel into your float bowl through too large of an orifice, you're going to have a higher level than you should...not just for a moment but constantly. It is all a balance, too. If your fuel level is too high, then in the B, you're going to have too much fuel up in the jet mast and that means you'll have too much fuel too close to the suction which means you'll run richer because you'll have more fuel to air than you need. Carter understood this very well and if you study Carter YF "seats" you will see they also incorporated a standpipe to alter flow dynamics and provide a more correct fuel supply.
I mentioned your toilet bowl. The regulator in there operates not simply as an on/off float activated mechanism but also as a flow regulator. Watch the water going into the overflow tube for an example. It has nowhere near the amount of pressure an open faucet would have nor nowhere near the flow. But if you got in there and drilled things out and modified your cutoff mechanism, I'd be willing to bet you could make that hose have so much volume (and pressure) it would fly off of its little perch and spray water everywhere it wasn't supposed to be going rapidly. Your carburetor should be trying to do the same thing. It should all be balanced so that your float is performing its job comfortably and not having to try to slam shut against too much input.
