My experience of jetting my own bikes, and reading others experiences too, is that there is no “exact” setting. All bikes are different, there ar lots of other variables not just the pipes; fuel! Weather conditions, engine porting, air filters..... my advice would be to get the bike running and carefully test the mixture at the various throttle openings i.e. idle, quarter throttle, half throttle and finally full throttle....the main jet only affects half throttle to full throttle so just messing with that is unlikely to give a good result. If you are experienced you can hear and feel how the engine responds to throttle. You can also try plug chopping, its takes time and knowledge to get it right. If you dont have the experience you could always take the bike to a 2 stroke specialist tuner with a dyno and get him to set it up for you. If you decide to do it yourself Its safer to start with rich settings and go from there, it only takes a few seconds of full throttle to wreck your motor if you get it wrong. Start with a big main jet, lift the needles, set up the idle first and progress from there. Good luck.