First off, because ya all are on treads dont mean theres no prep, proper prep on treaded tires makes a huge difference. Secondly a clone with a big pipe is faster than a LO206, and small pipes are a little better.
You say theres an RPM difference, newer karts with a proper set up can have a big difference over an older kart, with both on same gears. Also weight plays a factor.
Just too many variables here to say whether or not there is cheating.