I disassembled the valve unit and put it back together seeing nothing wrong. It now shoots eratic as far as power goes , misfires alot. Sounds like a dirty valve/pipe. I blew all passages out with lung power. Should I use compressed air ? I would sure like to solve the problem, as this my favorite airgun when it is functioning properly. Any ideas ?

I usually use brake cleaner from the spray can when I'm cleaning/degreasing my airguns. But you have to keep it away from plastics and some rubber, and painted surfaces (like the finish on wood stocks). It's also very flammable and you need good ventilation.

Check the firing mechanism - springs, hammer, pivot pins, trigger, etc. Make sure they're all clean, lightly lubed, and moving freely. One problem I had with erratic power was because the lube I used on the firing mechanism was too thick. It was actually slowing down the strike of the hammer against the valve stem. I cleaned it all up and switched to a lighter lube and he shots became more consistent.