Radiator flow

John_195

Hot water rads in an 1870 house.
2nd floor bedroom difficulties.
Radiator is first on lope serving 2nd floor so what is plenty hot.
Room was overheating even though room was very drafty. Most likely b/c t-stat was located elsewhere.
Sealed most of the drafts.
Replaced radiator with one about 20% small.
So i thought I was moving in the right direction. Now I am in an underheat condition.
I also replaced the standard radiator valve with a traditional ball valve. Is it possible that I am moving too much water too fast through the radiator to transfer enough heat? Radiator unit does have consistent heat from top to bottom and side to side.
What other risks are associated with running the valve full open?
Any thoghts would be greatly appreciated.