Try it with a 4 gas exhaust analyzer or better yet, a water manometer plumbed to the air cleaner cover to measure the pressure drop across the filter element- - - -it's not RPM; it's the venturi vacuum in the carburetor that concerns me when using a too-small air filter element. Getting enough fuel isn't the problem- - -it's all about having a free flow of air to maintain the correct fuel/air mix for best efficiency, power output, and gas mileage.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!