I have a Bad Boy mower with a 25HP Briggs and Stratton V-Twin engine. The mower is 2 years old and has about 62 hours on it. Recently it has started surging/hunting with the RPMs. When it is under load it smooths out. I am at a lost. So far I have down the following:

1. Changed spark plugs
2. Changed Air Filter
3. Changed Fuel Filter
4. Changed oil and oil filter
5. Cleaned the carburetor (it was spotless)
6. Sprayed carb cleaner to check for leaks
7. Checked the fuel pump.

If I disconnect one of the cylinders, the engine runs fine (doesn't matter which cylinder). I briefly got it to smooth again (not sure how), but than about 30 mins later it starting hunting again. I have not pulled the value covers to check the valve gaps yet, as I am waiting on new gaskets before I check the valves.