Hi Dave
If the block ports have been modified, then this might account for the noise if the exhaust port is opening earlier. If this is the case, try lifting the needle 3 notches, go up to 230 on the main jet from the 170 / 190 standard and try fitting a temporary restrictor in the exhaust, say about one inch to give it some back pressure. Some modern silencers are too big and free of impediment. Consider the Howarth with its more tortuous gas route and then the area open on the fish tail. They went well with this restriction.
A modern two stroke has a very small bleed but adventurous port timings. Try it and see and let us know how you get on
Kind Regards
Roger
