JERSEYSPIKE

I've got a problem with my aerox 50 2003,i have just had an engine rebuild, they have done the crank and crankshaft,put another big bore 70 kit on.I have just got it back from the bike shop and it goes nothing like before,there is a big difference in power before it went up hills at 45-50 now i'll be lucky if it gets to 35 mph and there is no way near the acceleration it had.The bloke is saying because it has a different make of big bore 70 kit that makes a difference,because the set up is for the other 70 kit is he right or is he just fobbing me off with crap.Can anyone help me.Cheers P.S thanks for all the ones who replied to my previous post.

I have a Aerox 50 2003 and has 20,883 miles on the clock, it has been de-restricted,and i have had fitted a big bore 70 kit, multivar, viper exhaust,and most recently i have just had fitted a kevlar belt and new rollers, the bike came back with excellent acceleration and top end, on the bill they have noted that the the engine has started to show its age with the start of suspected main end bearings about to go. The problem i have is that it has developed a bad misfire which i thought was the coil as i wasn't getting a good spark,after fitting a new coil,lead and cap the misfire is still there,has anyone out there have an idea of what maybe is wrong.Cheers Jerseyspike