I have switched out the sillenoid in my murray 12.5 hp riding mower and it will not start. It tries when you touch the points on the sillenoid but it won't completely turn over. What could be wrong?

If the battery is fully charged, it sounds like you might need a valve adjustment. I would first check the oil level to make sure it hasn't filled the crankcase with gas though.

Battery connections from starter to battery may have a bad connections.

Also check for safety switches under seat. The solenoid switch must work from the ignition switch not jumping the soleonid

Starter may be pulling too much juice. I like to physcially test the starter. I use jumpers directly to starter for that.