How do I get my MTD 8/26 Snow blower to run (again)?

I have an older MTD 8/26 snowblower. It ran this morning for about 3 hours and then started running very rough and stopped. It has new gas.
I prime, turn on choke, raise throttle and hit the electric starter. The engine starts with the choke on and immediately cuts out when I torn the choke off. With the choke on it runs for 5-6 sec. then shuts down.