Has anyone managed to improve performance on a Sym 125 4t motor

I have recently picked up a 2016 Sym symply 2 125 4t for a cracking price. It runs really well and the bottom end is pretty strong but it really struggles with top end, reasonably quick to about 35 but max revs take forever to reach.
Has anyone been able to squeeze any more performance out of these things. I was wondering whether they are running lean for emissions and whether richening the mixture would improve too end.

 

Yes a slightly bigger main jet but you need CC's, try to find a 150-170cc barrel, performance exhaust won't help much.

 

Thanks, I have found big bore kits but not sure if they are actually suitable for my series 2 as I can’t seem to find out what engine I actually have.
Same goes for the jetting as I can’t find anywhere what the stock size is, hopefully the original will be stamped if I take the carb off.