I know this is an old post but check the diaphragm in your model 60 mixer it probably ruptured from the backfire

You also need to check the timing belt. Could have jumped time or broken the belt.

Hi Gator,

When a truck starts backfiring and becomes hard to start in my experience it usually comes down to a weak fuel mixture. What op fuel system is on this truck. Check the fuel lock off filter for being blocked with heavy ends and clean vaporiser.

Regards Nero