Blower idle hunting, cycling, surging, annoying...

Hi all, we had the same problem and set the butterflies to 10-12 thou (smallest to largest) and played with our leak until we got it manageable. The biggest issue we had was a crap converter that was pulling the engine down too much. We have fitted a fresh converter and the hunting has decreased and is now manageable. 509 BB Chev, Dart 360 heads, BDS 10-71 at 44% over. We run 6-8lb on the idle, 28 on the port, 70 on the high speed. Waterman little bertha 16gpm, pump bypass 12lb. Cheers Graham

 

sorry, forgot to mention, we had a leak under that hat and could not get the idling right, it was too high but not hunting. The bolts at the front of the blower are quite hard to get to and had worked their way loose over a few meetings. I now check them on a regular basis. I use a small amount of silicon to seal it but dont run the screen as I had been told it was restrictive.

 

The 7AL may be a clue. Distributors with centrifugal advance and blowers do not mix and will in fact cause idle hunting. Lock out the advance problem solved.

Make sure the throttle stops on both sides of the shaft are set the same as vacuum/suction will twist the shaft and close the butterflies on one side bringing the idle down causing loss of suction to untwist the shaft idle goes back up shaft twists again.

Also check the butterfly screws and make sure they are tight.

Otherwise I vote for the Gore barrel valve. That old square valve is an antique and takes to much hand file work on the idle slot to get it right.