Nowadays most Birkys has either a 50 or a 57 on them if I am not wrong. Then Kevin makes adjustments inside the clutch depending on engine you are gonna run. Outside the clutch once set you are not gonna have to touch anything unless you have a n emergency like your clutch needs rebuild and is not engaging as it should, then sometimes you could make it work adjusting the springs from outside but in general as Chuck says just change ATF and ready to go. Mine for the stroker 131 Sudam has a 50/20 primary (20 on engine) and on the secondary I have run everything between an 18 to a 26 depending on track. Very rare to go to a 26, it was a huge oval, and for 18, 19 and 20 it has to be a verry small oval. Otherwise you are gonna be using 21-25 on the secondary with anything between 55 to 70 on rear axle. Only thing Birkys don't like is misalignment. Check your mount/jacshaft is perfectly aligned or you'll start melting belts. Don't ask me how I know, lol.