Small Engines (Lawn Mowers, etc.): Engine speed, briggs stratton, hp engine

Question
I am using a Briggs & Stratton 20-hp engine in my hovercraft for lift. My query is what is the maximum rpm that I can expect from the engine? It is used straight from out of the box, oil filled to the recommended level.

At the moment, I am getting only 2,300 rpm although I was told that it should be 3,600 with the speed governor, enabled.

I wonder if there could be something that I have not removed or adjusted before starting.

Or could it be that the fan is giving excessive load to the engine? I want to run the engine without the fan but was told that I should not run the engine without any load. Is this true?

Answer
Hello Yahaya,

The engine should obtain 3600 rpm.  I'm sure you have tried adjusting the high speed mixture screw, if present.  Next, look to see if the throttle plate is opening fully.  If not, you can adjust the linkage or bend it to give full rpm's.  The engine should have the power to handle the fan's load, if designed correctly.

Let me know how you make out.
Michael