Kohler 15hp engine makes knocking sound at high rpm

[CharlesR]

Got an old Murray lawn tractor from a shed where it had been sitting for 7 years. I finally got the Kohler CV15s engine running, but now when throttle is over half speed I hear a knocking sound. Sounds like something out of balance or maybe backfiring? You can listen to the engine at this YouTube link:

Murray Lawn Tractor with Kohler CV15s engine knocks - YouTube

Work I have done so far:
Rebuilt carburetor, replaced all other fuel system hoses, filters, etc.
Replaced spark plug.
Changed oil filter and oil.
Replaced air filter.
Any help of this would be appreciated

 

[KennyV]

Look under the engine at the belts... it sounds like they bouncing the idler pulleys around... don't get anything cough in there
while looking around...:smile:KennyV