PX 200 Nipping up

I have a Vespa PX 200E year 1998. At the moment the main jet is 122 but after a while at full throttle the engine is nipping up. Advice given is to up the main jet to 124 and change to a B9 b8es spark plug. Does this make sense

 

It currently has a standard barrell and piston, a dell orto SI 24/24 E carb, main jet mixing barell Be3 122/160 and idle jet 55/160

 

It has a JL stainless steel exhaust, exciting on the left hand side. (Looks like RZ Evo 2000)

 

 

Used in Ireland mainly for short runs.