We just purchased a house and the bathroom was remodeled about 8 years ago. There is one annoying issue: the tub faucet lever only rotates less than 90 degrees and if you want cold water it will only trickle. If you want warm or hot water it's ok but I would like more control over flow and temp.
Do I need a new cartridge? Or is this a easy adjustment?
You need a different style faucet if you want separate control over temperature and volume (flow). They have two different knobs on them. What model is the faucet? Some brands (delta i think) use the same valve for all types of faucets, and all you would need is a new cartridge and trim piece to convert to this type of faucet.
Look at this pic, if you look closely, there are two knobs: