Hesitates when secondary on Holley 4160 is open. Convert 4160 to 4150 for more fuel?

[Gasoline]

Hello! I have a question about my Holley 4160 600 cfm sitting in my mustang fastback 1971. The car has a 351W engine with high performance cam and a 3-speed manual transmission. I works great during idle and normal acceleration, but hesitates at cruising speed when secondary port is open. I had a company test my mallory 27 distributor, new ignition coil, new fuel pump, fuel filter. Vacuum at idle is 15 and there is no leakage. I have checked the carburetor and replaced gaskets and uppdate jets to 68 (earlier 66) and changed pump cam to red (second hole) after testing different variations. It was earlier orange, but response is much better now and it doesnt smell so much gasoline anymore I´m guessing that there is not enough fuel for the secondary port and thinking about buying a holley conversion kit metering block so I can use different jets. Such as: http://cgi.ebay.com/ebaymotors/Holle...=p4506.c0.m245 I this the solution? I also have to change the spring to a stronger one because there is a slight bog when the secondary opens. But my concern is the hesitation when driving and not pressing hard enought at the gaspedal. Going down the highway is less problems. Thanks, Thomas (Sweden)

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[my77stang]

i added the secondary metering block to mine and i think its probably the only way to properly tune the vacuum secondary carbs.