Hey guys I was wondering if you had any recommendations on jet sizes to use for my 250. I have a comp cams 260H .040 over pistons Port and polished head with bigger valves, Offey intake and headers. Its a Carb of one of my V8's (350 I think). Anyway I know it probably doesnt need 600 cfm and I would like it to get good fuel mileage as well. Any help?

A 390 OR 450 WOULD BE ALOT BETTER FOR YA.

I have about the same motor and ran a 600 for a while. I took a tie wrap and tied off the rear linkage and ran it on the front half (about 300 cfm) Doing that made a BIG jump in how it run !!!

I've done a lot of carb swapping from v8's to the chev 6 and never changed jets at least not for just that reason. OF course other stuff affects jetting like air temp, headers, etc but not number of cylinders at least in my testing. So I'd go with about a 65 primary jet and see how it runs. In the 600 Holley Ive used everything from a 62 to a 68 jet depending what the combo wants.

Agree a 600 is a bit big for your motor but (see "new guy with engine" thread, if your minimum RPM is about 2400 or more it should work okay, free is a better value than a new carb!