Both the "On" and "Reserve" positions on your petcock are vacuum powered and only flow when the motor is running or cranking over at least. It will take forever to fill empty carbs that way, lol. You need to set the petcock in the "Pri" (Prime) position. This setting bypasses the vacuum function and just flows like a normal petcock. But don't forget to switch it back after the bike starts because the "Pri" position pulls fuel from the Reserve pipe. If you run out of gas, you will be really out, lol.
Stainless spokes are quite reasonably priced for these bikes compared to most others. I prefer the aluminum alloy rims because they'll never rust and I like the look of polished aluminum vs. chrome. More maintenance, yes, but I just like them better. I think you have the bazillion spoke Heritage wheels on yours? I don't care for the 72 spoke front, I just don't like the "look", too many spokes. I built a regular 36 spoke replacement for my '83, and used a wider rim as well (2.15 vs. the stock 1.85). I really like the way it turned out and the way it looks .....
For the rear, I can handle the 48 spoke Heritage wheel, so once I wear the tire out, I'll be rebuilding the wheel with stainless spokes and an aluminum WM type rim to match the front.
The wheels all swap on these from '73 on, so you might keep an eye out for some alloy rimmed replacements. If you wanted to switch to mags, you'd need to find a rear drum type from an '81. That's the only year that came with a rear drum mag. For the front, any year mag will fit and work ('78-'81).