The first people with a 170 kit lifted the cylinder 3mm, hence the terrible torque curve..but from then on the myth that the 170 kit needed 'port adjustment' was set in stone..while it benefits from porting, lifting the whole lot 3mm is a bad idea...The Athena 170 cylinder is the same casting as the 125 but bored out to 65mm. Most people reported a good increase in bottom end grunt but no real gain at peak hp. It turns out this is mainly due to the cylinder casting being the same as their 125cc cylinder, so has 125cc sized ports.
I opened them up to 170cc sized ports by widening the exhaust
5mm, and lifting the transfers 1mm using a 1mm base spacer
and 1mm skimmed of the top of cylinder. It is better raising the
cylinder rather than modify the transfer ports as the Nicasil
plating chips easily.
Double check the pv cable setting. On mine with the pulley
lined up with the mark, it was only about 3/4 open. Only when
I looked up the port did I spot why it felt so flat initially!
Initially the 170 kit felt awful, until I double checked the pv
setting and found it was about 3mm closed. Once that was
reset, it flew...