Does changing port timing affect air/fuel ratio?

[CuriousJojo100]

I don't remember the exact CC of this specific motor. I do know the piston is bigger than the standard China girl

 

[CuriousJojo100]

I have worked on enough of these 49mm cylinders to know that is the 49mm bore/72cc, correct?

I love port timing and know these cylinders specifically like the back of my hand. I can answer any questions you have specifically on this top end.

I believe it is

 

[CuriousJojo100]

I cleaned everything from the ports. Better power throughout rpm range. It falls on its face near 5200rpm for a few seconds then the exhaust note gets a lot more raspy and the powerband kicks in but I find it kicks in too high in the rpm range. What are my options to lower the powerband about 1000rpms?