Hello - I just bought an 81 XJ550 Maxim and had a similar problem. The bike starts well, but I also had to hold the choke down for several minutes since the bike kept stalling. I peeked under the gas tank and noticed an idle adjustment knob. I turned that knob couterclockwise and increased the idle to about 1500-2000 rpms. The bike now runs on its own without stalling. Hopefully this helps!