I just bought a 1980 yamaha 650 special that had been sitting for 30 yrs

Do you have a synchronizing tool? If not, you'll need one, either homemade or store bought. All what synching the carbs means is that they are both pulling in the same amount of gas and air based on manifold vacuum pressure.

check the rotor magnet to see if the windings are shorted to the base use an ohm meter to check for grounding to the base.

hi,anything will fit with the right equipment on hand to make modifications,but you will probably find the xs seat will be to wide and deep to fit the  frame rails of the xj

there is not much difference between those 2 engines. they are the same cc and both are in-line 4 cylinders.

30 thousandths.

you should use a good quality 10w40 motorcycle oil