sirtopemshat

this is my first bike so im sorry if some questions sound retarded. I got a 76 xs360 a while back. previous owner hardtailed it with a stretch and didn't seem to care much for anything else on the bike. it runs well, but has a few little quirks id like to fix. first off, once warmed up sometimes the idle surges high. what causes this? Another question is there seems to be a pretty annoying tight spot in the chain...does this mean the chain needs to be replaced or sprockets, or both? also, when the battery is charged, the bike kicks over fine, but if its dead, it seems like the motor isnt making anough voltage to get a good spark. i always assumed you could kick a kick start bike even without a battery, or am i wrong? is this a charging problem? this is usually only a problem if i havent run it in a few days. last questions as far as parts. what are good sources for parts? how much part interchange is there between 360, 400, and 650? im also looking for a small speedo and tach like mikexs sells for the 650s. do these bike use the same cables as a 360? i need new speedo and tach cables as well. thanks for any help.