Start it up, richen the HSN until you can hold it wide open and it's very rich. Run 3-5 tanks. On the .21, you richen the HSN two full turns, but I don't know for the .12.
Run it 4-5 tanks on the track at a rich setting, not going full-throttle down the straightaway or death-revving it over a bad jump, but otherwise drive it like normal. After that, you can spend the next tank or two tuning the engine to achieve race performance.