Bought a sports exhaust but have no power help

exhaust my mate got on his jinlun 50 with a 80's kit but haven't got top end any ideas lads

 

well...i put one of them on mine and had no bother at all..but like Stevep said in the kev Clark post..might need a bit of a jet change..if you've done an 80 kit too.ive got an 80 kit for mine but never got around to fitting it and it came with an 84 jet...ive changed my carb for a 19mm and it needs a 6 mm jet..80 kit was/is 5mm.aint got a clue what the 19 had got to start with so my result might be down to having a bigger jet to start with..got an open filter on mine too so I think I'm lucky it still runs and does about 38on a long flat and touches 47 down hill...indicated...true speed is anyone's guess.have a go at changing the jet up 6 and if it improves,keep going up till it goes a bit iffy and drop 1 from there..if that dont help...try the other way...you never can tell with these chink motors

 

We've up-jetted the standard carb with the 84 jet starts and idle spot on, we'll be putting a Motoforce clutch in, will be changing belt, torgue spring, cdi box and will be changing the carb at some point either to a 19mm or a 21mm+

 

I've put a thread up with the bike on under jinlun jl50qt-4

 

I have found with tuning up 4 stroke engines just a exhaust will not make any difference other than noise. There not like a 2 stroke where a exhaust and carb will make a massive difference with the 4t engines you need to do everything you can from bore,carb,exhaust,cam,valves,variator,clutch,cdi unit the list goes on... They cost more to tune up but you do get longevity from the engine.. 2 strokers are cheap to tune and get the most out of parts on a budget.
I am not sure what the market is like for chinky tuning parts as I would never have one after fixing to many of them and there cheap build quality.