Small Engines (Lawn Mowers, etc.): 20HP Onan - Losing Power, carburetor, good luck

Question
My old Onan seems to be losing power when I engage the mower.  It runs good and does not smoke.  It starts very easily and uses only a small amount of oil for its age.  Could the power loss be caused by valves that need adjustment?

Answer
 Hello Mark:

 Yes, the Valves out of Adjustment will Cause Power Loss. The Carburetor will have the Same Effect if it needs to be Cleaned and Rebuilt. Hope this Helps. I am here if you Require more Assistance. Thanks.

 Good Luck

 Respectfully  

 John