150 grit sand paper... I use a harbor freight variable speed 7in buffer and use the hook and loop 7in sanding disks from there also. Took a class this spring at a local kart shop and thats what they said to use. Maybe somebody else has a better way but thats how id do it if i ram asphalt.
Internal prep, amount will be conditional on the type of weather your racing in and time of day. No prep on the LR, it’s just meant to hold the left side of the kart up. Like said above definitely heat gun and scrape them before your heats and feature. I’ll sand them during the week with either 40 or 80 (depending how chewed up the get) and finish with 150. Harbor Freight 7” vari sander is the way to go, grinder spins to fast and over heats the softer Vegas.
We take them out of the wrapper and go, generally depending on what division we are racing on the particular weekend we are on. Sometime we are considerably faster if we scuff the tires and put
Them back in the trailer for a week. Before you go crazy prepping try a few sets new or scuffs.
Your HL2 would make an ok internal prep for them.
If they're fresh/new thin right sides, you may need nothing internal.
Personally, I prefer to use our Medium Rare internal (2 ounces in the RS and 1 ounce in the LS) with Vega Yellows on pavement. It helps condition the tire over several heat cycles as the oil is pulled to the surface of the tire.
If the track is tearing up your tires, and/or you are building too much heat in them, then our internal will help as well.
Scuffing a set or two and letting them set up a couple of weeks will be helpful as well. The scuffing and running a heat cycle through the tires will "toughen" them up a bit and they will harden a touch, which will also help.
Definitely scrape them clean with a heat gun after each time you're on the track. It will not hurt to sand/refinish them at that time as well.
Use just course enough to remove the left-over dead rubber/clag, dirt, etc from the tires, then finish sand with a finer grit to leave a plateau finish (similar to honing an engine cylinder.) I use a belt sander and plenty of Windex non-ammoniated window cleaner as a coolant. I am happy with the resulting finish.