Welcome!
First thing: look inside the tank for rust. If it rusted, then get the liner kit from POR15, best of the best. Come back for more details on how to use it: once used. this lasts a lifetime and stops all rust forever. DON'T use the one called "Creme" as our modern ethanol-blend gasoline makes it come loose from the metal, and it can ruin the tank's petcock and the carb jets.
I'd recommend going to your local auto parts store and finding a points file: the points are likely slightly rusty. DON'T replace them, at least not yet: they are semi-self healing after 100-200 miles in use, designed to be that way. Modern points must be bought directly from Honda, and I recommend South Sound Honda (buy the entire points plate set, about $80) if you decide to replace yours: otherwise you will likely end up with the impretinent Daiichi points and condensors, which will park the bike with electrical troubles.
First thing after all this: once the tank rust is corrected, fill the carbs with gas (just open the petcock, let them fill up) and then drain them, repeat. Maybe 3 times: this will move most of the crud that has collected in the fuel lines into the float bowls, or at least as far as the float valve in the carbs. This may necessitate removing the carbs to remove the float valve to clena them out, but will solve the problem. If you decide to 'rebuild' the carbs, then ONLY replace the rubber parts and not the brass jets and needles. The OEM parts are fine. All currently-available brass parts are not calibrated correctly, and most of the 400F problems I have come up against these last 10 years have come from non-Honda (Keihin) parts in the carbs. The solution has been to reinstall the Keihin parts to get the bike running right again. These parts last a [your] lifetime, no need to change them: the only ones that might someday need changing will be those float valves, and many brands of those will work fine in these carbs.
When you get it running, it will likely be 'rough' and low on power for a little while. The valves are likely a little rusty, but the way these engines are designed, they will 'self heal' quite a bit if ridden often enough. It may take 200 miles for the performance to all come back, so be patient and resist tearing things down, so ong as the engine still turns over now. If it is stuck, you're in for a bunch more work...but we can help!
