I have a 502 with a B&M 250 with dual Holley 750's. The carbs were set up by pro-systems, and are boost referenced. The jets are 74's all the way around with 5.5 power valves in both the primary and secondarys. The engine was a 500hp carb, but now has flat top pistons in it. I took the new engine out for a test ride yesterday, and the plugs were reading very lean. I have dual fuel pumps running to a manifold, and then to the carbs with 7.5lbs of pressure. Just wondering if anyone has an idea what I might jet these at? and do the power valves sound right? Was going to start with 78's all the way around to start with.

Apples and Oranges...but I have a procharged 454 running 9 lbs boost. I got rid of the plug fouling problems and low end torque when I cam down to 78's on the front....am running conservative and have 102's in the secondaries! I don't know what my power valve is. I know there is more left on the top but think I have my midrange within 90+% of potential and I should be safe!

PS Mine is a single 650.

Are you sure its a flat top piston? unless the combustion chambers are pretty big I would thnk that you would have too much compression with a flat top? that may be why the plugs showing lean.

How much boost ??? When I had a similar setup, I ran 82 prim and 94 secondaries.

Looks like we have a spammer !!!! ^^^^^^^^^

i'm running 6lbs of boost with this setup.

Where? I read that as 80 primary and 92 secondary.....its just written in a secret tuner's code

i really hate them fargin uggs

are you checking fuel pressure under hard run ? need to...if thats fine...read the plugs and tune from there..I have been running prosystems carbs for years(and still am) and they are usully real close out of the box...but close not always perfect...tune from there..

put a a/f box on then you will have the reading on your a/f no guessing