Featherweight
 

I am having trouble getting it to run after changing the belt. The motor is going wheel going but the belt not moving.

1 of 2 things.
Either your belt isn't tight, either adjust it or get a shorter belt. Or, the belt is tight enough but your machine is stuck somehow.
Chances are it's just the belt. I don't own a featherweight so I'm not sure exactly how to adjust your belt.
Rodney

So are you saying the belt is slipping?

If your belt is too long you can adjust the motor position. There is a screw that holds the motor up. The screw head faces the front of the machine and can be found lower than and behind the handwheel. You can loosen the screw and the motor will drop. You just want it tight enough that the belt grips but you don't want a lot of tension on the belt. It should not be tight, just enough tension to get the belt to grip, if I understand correctly. I had my LSMG put mine on and he adjusted it for me.

I just put a new belt on mine, an original style black v-belt, and the new one is a bit tighter than the old one was. Per the manuals, I just let the loosened motor weight the belt and tightened it there. Which was fine for a few minutes of use until it stretched out and lost grip and I had to do it again. And will probably have to do again when the belt wears in a bit more. I basically made it just a bit tighter than "just tight enough to work" but it still has play (dropped the motor a little bit more).

Otherwise, make sure you've put the hand wheel and stop motion assembly back on correctly, stop motion washer tabs facing out. Mine was on backwards when I got it.