I have a MTD rider mower, I used it a few weeks back. Mowed for 30-45 minutes. Ran out of gas, put gas in it hasn't run since. Checked to make sure it is getting gas that's not the problem. Cleaned the spark plug (had fouled) but couldn't get any spark. Pulled the cover off the engine took sand paper to the flywheel & coil pack still no spark. Seems to have power going through all wires and all grounds seem good?

Unplug the wire going to the coil.if no spark bad coil . If have spark check switch and ground wire going to coil,
Luck

Changed the coil has spark now. Cranked it over got it to run for about 30-45 secs then it died again. Still has spark but still won't start. Battery acts like its dead. Put jumper cabels on it to the 4-wheeler and it cranks over but no start. Checked voltage on battery it reads 11.8 volts. Not sure what to do next.

Spray some carb cleaner in the carb see if it starts , if so check carb , might need a good cleaning
Check fuel solenoid on bottom of carb if it has one.
When you installed coil did you gap it at .010 or a business card between the coil and magnet.
Luck

I gaped it with the card that was supplied by briggs & stratton that's what it said to do on the instructions. I'll check the carb, thanks. I left the battery out overnight it reads 11.6 volts today.

Got some carb cleaner, new fuel line, fuel filter, drained the tank & cleaned it out. Took the carb off didn't look thast bad. Finally got it to stay running. Mowed most of the back yard before I ran out of daylight. Thanks for the help.

Your welcome ,good job ,