Small Engines (Lawn Mowers, etc.): lawn mower still not working right, oil cap, connecting rod

Question
Hi John,
I'm sorry about the confusion. Let me try to explain what it's doing better. The sound it's making is like a knock and also when I remove the oil cap the engine starts reving. I don't know if that's normal. The lawnmower is usually quiet and runs smoothly but now it's like a knocking sound in the engine. The blade is the original blade.
Hope this helps
Randy

Answer
 Hello Randy:

 Thanks, That helps 100% more. The Problem is either of the Following: 1- The Crankcase Vent is Clogged. This Allows Pressure to Build up in the Crankcase and Restricts the Piston. 2- The Engine has a Cracked Ring which Allows Too Much Compression Blow By and again the Piston is Restricted. 3- The Knock is the Connecting Rod; provided the Engine Isnt Over Filled with Oil. If the Engine is Over Filled with Oil the Piston will Hit the Oil and make a Knocking Sound like the Connecting Rod is Bad. If the Oil Level is Correct and it still Knocks, then the Engine is No Good. Hope this Helps. Sorry it Took so Many Times to Figure out the Problem. But wanted to be Sure.

 Good Luck

 Respectfully

 John