Main jets are usually too rich, so they grant a temperature reprieve. at full throttle The most important are the needles and needle jets - they are in use as you accelerate and change up through the gears., If the exhaust is too restrictive, the cam might not work properly, so you are down on power, but comply with noise rules - your choice. For normal suburban use, the main jet sizes are pretty much irrelevant, but on a freeway where the throttle is held wide open for long periods, the main jets are still better if on the rich side.
If you have reduuced the restriction of the exhaust, the jetting will usually lean-off slightly. If you ever get the cough when you are changing up theough the gears while accelerating - that is the sighn the jetting is too lean. Do not continue to ride the bike, but richen the jetting by raising the needles.