GreekPhil

Thank you! This is my first time on a forum so no clue how they work hahaha!

So I bought my first bike (Yamaha YBR 125) last month, and yes I am aware it is a slow bike but so far I was happy with its top speed performance which i got up to 73 mph. Yesterday I took it for a service as the people before me had not taken it for one so naturally i thought i was due one. After I got it back from them the gear changes felt smoother the braking was better almost everything was improved. However the bike now just about manages to get to 60 mph in a straight line, and 5th gear (top gear) feels no different to 4th gear, the only difference is the revs go from around 9000 to 7000 but the speed stays the same. Also I have noticed the exhaust sounds more quite and it almost never backfires now. Could anybody help me with this? As you can see I am a complete novice Cheers guys!