What should I do to adjust my watch (Omega - 40's?)

[BMWChris]

My wind-up Omega has a lever inside that goes from A - R. It kept time very badly and when I opened up the back I saw that the lever was all the way over to R so I stuck it in the middle. This improved things but it still gains about 4 minutes in 24 hours. I'm not sure what is normal for a watch of this age.

What should I do with the lever?

Ta