What should I do if I cannot complete the same reps/weight with my left arm v right arm. should I use different weights on each arm, or stick with the lighter weight until both arms are equal.
You don't really want to encourage the imbalance. It is best to start with weaker arm and stop when the weaker arm fails. For example, say that you do 8 rep with left arm. Only do 8 with right even if you can do more.