Small Engines (Lawn Mowers, etc.): mtd snowflite 20 snowblower, shaft, 30 minutes

Question
Have a mtd snowflite 20 model 310-100a. It starts well runs well. After running more that 30 minutes when the engine gets hot the engine revs really high. Unless I keep it working and throwing snow it revs extremely high. Not sure what to do. Am not able to find manual for it.

Answer
have you tried  mtd. com????    also try these >  m-and-d.com   
make sure the governor shaft is not getting loaded with snow.  or is clear of anything stopping it. the part where it runs okay for 30 minutes baffulls me...   and i have no books on this... tell me is this a 2 cycle or 4 cycle.???  and do you know what engine??