How to derestrict peugeot trekker wrc 2004?

I have fitted different exhaust(with the tube removed) i have fitted a bigger main jet (from 52 to 78 )i don't want this to go too fast just have a bit more than 30mph,i have replaced the rollers with the same weight but new( the old ones were getting flat in places).
The problem i have is it still only goes at 30mph and it is hesitant until it's warmed up,is there anything else i can do to get a few more MPHs