I'm sorry, but disconnecting the vacuum advance is a terrible idea. When my C60 bus still had the original 327, I switched it to HEI when the original governor failed and wouldn't let the engine rev anymore. Vacuum advance is there to be the load sensitive portion of analog timing control, only retarding to what's in the mechanical weights under heavy load. A properly set up vacuum advance improves drivability and yes, even in a C60, can net you another mpg-and from 6 to 7, that's not nothin'. I remember when some old boy told me to run it with no vacuum advance.. yeah, it was fine wide open, but throttle response was pretty mediocre at more moderate loads, and it was actually kinda gutless off idle. As soon as I hooked the advance back up, I found I didn't have to put my foot all the way in it to accelerate, and moderate loads needed a lot less foot feed to control the rig.
I know I'm disagreeing with the powers that be, at my own peril here..
but this is my two cents worth.
When the advance unit failed, I inadvertently ran the Cadi engine in my bus with no vacuum advance for a few weeks.. couldn't figure out why I was suddenly down from 7 to five mpg!
