Legend has it one former poster on this forum (something of a legend in his own mind, IMHO) "ported" his way into the water jacket of his KLR650 head; then blamed the profound, true expert who had instructed him, for the "amateur night" mistake.
Porting and polishing remains to a degree an art, as well as a science. Top professional engine-builders sometimes use FLOW BENCHES, at least to get ballpark knowledge of cause-and-effect results.
Finally, a correctly ported/polished head may yield power gains at 6,000 rpm; at 3,000-4,000 rpm, typical KLR650 service-life operation? Not so much, IMHO. In fact, as Klahowya41 mentions above, without sufficient turbulence at certain rpm/flow rate operation points, a ported-and-polished wonder may yield LESS power than a stocker.
Similarly, OVER-CARBURETION is POSSIBLE; a too-large venturi cannot permit adequate flow velocities and fuel-atomization turbulence to produce optimum power, compared to a properly-sized carburetor. [IMPOSSIBLE to convey this concept to someone enamored with the, "Bigger is ALWAYS better!" mindset, in my experience.]
Finally, miniscule gains in power (without measurable, repeatable data, and/or drag strip/speed trial runs), remain largely a function of, "head-space between the ears," of the tuner/rider, IMHO; YMMV!