I have an 8 hp snow blower motor that runs very roughly. When I tried to throttle it up, it runs like a Harley Davidson motorcycle barely idling. Further, once left for 30 seconds to 1.5 minutes of idling, the motor appears to kick up to full speed but backs down to very rough, low-power idling when the machine is pushed into snow. It is not an electric start. The motor is probably 10 years plus old.

Hi,
It is fuel/carb related problem. Without more info, that is about all I can say.
Peace,
Clarke