You can run a 30 series.
Its going to eat a lot of belts.
Trouble is with these cheap clutches they throw the belt out of the groove and slip at high RPM.
They get hot and slip too.
They eat belts as well.
DON'T use a PIX belt they are too soft..
Clean often and when you see wear glazing and groves on your primary take it off and stone it with a large sharpening stone to roughen the surfaces.
Use plenty of clutch lube.
I notice some of the primaries have a lot of slop in them.
I tin up the moving sheave with some 60/40 solder and hand scrape them to make a tight fit on the driver bushing.
I also make an extra long bronze bushing to take up the load as the primary opens and closes ( this prevent the slop from smashing up the driver under heavy loads ).
Heavier spring on the secondary is a good idea, adding a second helper spring might help too.
Heavier spring on the primary to raise the engage speed and trim to fit so there is no slack ( this trick will cause more belt wear at low speed however.
Everything you do to improve the TAV will cause more wear in belts and bushing.
The only way to avoid this is a light touch when you ride.
I think I am the first to run a 7 inch secondary.
You used to be able to buy a kit from BMI for the yerf dog go-kart.
Still a few floating around...
Jackshaft Plate Hub Bearings for Go Kart Mini Bike Yerf Dog Free SHIP | eBay
This is also a handy part to tune your clutch.
9T 40 41 Sprocket Gear for 20 30 Series Comet Torque Converter Driven TAV2 USA | eBay
You want this.
Comet Yellow Spring for 30 Series Driven | Go Kart Parts | Racing Karts | Engines | Frames | Tires | Tips | Kits | Torque
And the white primary springs if you can find them ( use 1 one or both to replace the stock ones if you prefer )