Sorry for the confusion...if you have a 38/38 it's not progressive...both throttle plates open at the same time...i have a 32/36...the throttle controls one plate...the other opens automatically as needed under full throttle...i needed that kind on my mighty 2.5
so it wont bog....you can get a regulator in most auto supply places..in the "hot rod" section...mine is adjustable from 2 to 8 psi..hope this helps..
Dawg[addsig]