If you increased the out flow then you need to install a larger main jet to not be running lean . Some stock pipes are made out of crappy pot metal that rots away and falls apart .
Would help to know if you have a 50 or 150 . Yes there most of the time will be a modest gain along with better sound too . You could drill two holes in the end or cut off the nozzle tip , bore out the hole and weld on a larger tip . To get the most out of a better flowing exhaust a Uni or K&N airfilter can do wonders , even more with a ported head with larger valves . Note exhaust mods as well as airfilter mods both require you to upjet and make take testing a few sizes out in order to fine tune it . I would get a jet kit which has several sizes and is cheaper than paying per jet price . Here is some
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