so, I have a mostly stock 1957 and distributor on what is 292 or possible a 312. haven't be able to confirm which. That being said it has a summit M2008-MV8600 carb. (600 cfm). Seem to run ok on primary but when you step it down the secondaries seem slow and a sluggish response but pulls fairly well. Is the 600cfm carburetor to large? Is it pulling in too much air for the fuel ratio. I opened the carb. pri jet is one size smaller then the stock show. Secondary jet are Stock size. Any suggestions would be helpful. the jet size on 500 cfm carb. stock is Pri. 62 & Sec. 68, the 600cfm Pri. 68 & Sec. 73.. Summit suggested you could run to lean on fuel and air flow would be same. might harm motor. Thanks