The 14/147/1400 rifles do present some challenges if you've never worked on them before. Getting the pump cup off can be difficult. There is also a small seal inside the blow off portion of the valve that if not replaced, will not allow the rifle to seal. This has been gone over many times before on this and other forums. I'd suggest using the search function and reading up on it before you tear it apart. They aren't hard to work on but you've got to know the tricks.
I'd also suggest losing the stock transfer port and instead use 1/4" poly tubing. That will give you max velocity with that gun.
"but I'll be needin' that gun, fer squirrels and such."