I just bought a Holley 390 cfm 4bbl to put on my 250 cid chevy motor. I have a Clifford intake and headers with an almost stock Comp Cam. Should I run the stock Holley jets and power valve. or what should I change to?

Good question, I should also buy a new carburetor. I should make decision between Holley 390cfm, Edelbrock 500cfm or Demon jr 525cfm. I have heard positive feedback about Holley.

I have used the 390 holley, but a double pumper version intended for competion use. Had to change jets, had a 290' Isky cam, 10/1 comp ratio, headders. Used the 6.5 power valve, but do not remember the jet sizes. The carb was very good in power, but fuel economy was not all that great. Had a lot of time trying a bunch of jet sizes till found the right one.

i have a sock cam in my 250 with dual exhaust, 1.94 int valves and about a 9.25:1 CR and i have to put size 55jets in my 390 so it would hesitate off idle or when driving...i also added the next size up pump shooter, but you dont have to do that.