I have a 66 Holley 4160 that I have added a secondary metering block to that ran fine and then it just wouldn't idle. I used the Holley 4160 to 4150 secondary conversion metering block. I had the metering blocks milled to make them flat and cleaned all the fuel passages. Still no luck. Again, It ran perfectly and then it seemed to run like it has a vacuum leak. It runs as long as you hold it at a fast idle. Any ideas?