I am rebuilding a Motorcraft 2100 for my 4.2. The internals had a decent amount of sand on the inside of the carb. The power valve feels gritty when I depress the spring loaded contact. I tried to remove the brass piece shown in the picture, but the piece it is screwed in(the shiniest metal area in pic) spins freely so I can not remove it. The contact works freely if the metal area is turned in the right position, but if I turn it 1/2 a turn the contact will only depress about halfway. Is this how this should work? If not, I assume this one is shot. What size is correct? I did not see a stamp on it. Where is a good place online to order?