Were you doing this to 2 strokes or 4 strokes?
I did quite a bit of "polishing and porting" on two stroke motors, with good results. Our work on 4 strokes seemed to show that enlarging the exhaust port did help, but any work on the intake ports was hit and miss.
The basic reason here is on a carbed bike, the size of the exit port on the carb itself is in fact the limiting issue. Even if you widen the intake port on the cylnder, the amount of fuel/air the carb lets in is restricted to the size of the opening of the carb itself. You can open the intake to match the opening area of the carb,..but most 4 strokes built in the last 30 years have intakes that are in fact larger than the carbs venturi. so opening them up does nothing, and can if fact "Slow" the mix to the chamber. Remember also that the area of the opening of the intake valve itself is a limiting factor. Intakes that might have smaller diameters than the carb still sometimes work better than opening them up...as they can sometimes increase the "venturi effect" , and can aid in the speed in which the cumbustion chamber fills
It was also found tha polishing the intake many times lowered power, the reason behind this was that the rough surface of the cast intake caused the mixture to "swirl" more, providing a much better atomization of the fuel..making it burn more evenly and faster. Smoothing out the intake removed or lessened this swirling effect , and power went down.
Now, increasing the area of the exhaust port can be helpfull, as it can make sure you are getting the full potential out of the intakes size. But again remember that the exhaust valve is again a limiting factor.
The best key here is to leave the intake port alone, unless you are installing a larger mouthed carb. Increasing the air flow by removing restirictive air boxes and jetting up to compensate does help alot.
But after doing this, the only way to see siginificant gains in power would be to install larger valves, and/or perhaps a less restrictive exhaust....along with opeing the exhaust ports if needed. And hotter cams, perhaps a supercharger or NO2 tank, rockets...yeah, rockets would work....LOL