If I ever get a small 4 stroke I have ideas, port and polish , different cam, boost the comp. rework the rings, racing piston if I can find one . rework the oiling system, run royal purple oil in it.
I've taken a stock 5 hp briggs and with do it myself mods get 10 to 11 hp out of them. I've made my own cams. I understand the cams in those engines have plastic cam lobes I think a guy could reprofile the cam by grinding them, anyway I have some ideas and just scraching the surface, but no engine. maybe some day.
the straight pipe would be more for eye candy but it might help. On a 4-stroke kart engine I'll paint the pipe and anypart that the paint is not burned off of gets cut off.poorboy way of tuning it.