As suggested earlier in this discussion your problem seems to be too much fuel in the bowl (excepting a crack somewhere). The cause is either: leaking float, bad/sticking/incorrect float pin, defective float pin lock or very excessive pump pressure. My personal experience with this more than once has been a sticking float pin. Make sure to use a new pin and that the pin seat is scrupulously clean. You can't tell by just looking at it. The tiniest bit of varnish can make it stick. The percolating you are now experiencing at shut-down may be heat related in that the fuel is at the top of the bowl and any latent heat causes it to expand slightly and overflow. The only other issue could be the float level set too high, but I assume you've covered that. Keep at it!!