Would anyone know any good basic mods like governer removal and stuff.
Disable low oil sensor.
Remove or Adjust Governor
Air Filter Adapter and Pod Filter
0.036" Carb Carb Main Jet
Aftermarket Exhaust Pipe/Muffler
Offset Flywheel Key (for advanced ignition timing)
Also I need to change my gear ratio for flat grass surfaces. Should I go 5.5:1 (12:67) ratio with a centrifugal clutch or 5:1 (12:60) with a torque converteror or what would you suggest I use.
I think you said before that you had 13" Tires. Is that correct?
I'd go with the Torque Converter.
Would anyone know where I can buy a cheap torque converter, chain and sprocket kit or a size 428 sprocket.
All help I greatly appreciated
Location, Location, Location...
The TC kit comes with a sprocket that works with #420 chain. Not sure about #428, but are you replacing the rear sprocket too? Not positive about a fitting a #428 chain on the sprocket that comes with the TC.
It comes with a 10T #41/#420 sprocket. If it were me I'd use it with a 54T #420 or #41 sprocket
Still assuming 13" Tires...
54T :10T with 30 series TC Overdrive = 4.86 :1 Ratio
5000 RPM = 40 MPH...

https://www.ebay.com/itm/Torque-Con...570.l1313.TR11.TRC1.A0.H0.Xfuel+injector.TRS0
Need a sprocket that matches the hub it bolts to.
https://www.gopowersports.com/sprocket-48-60-teeth-41-420-chain-dual-pattern/
https://www.amazon.com/kart-Live-Axle-Sprocket-chain/dp/B01LXBNM48?th=1