The Ford Barn

03-23-2005, 01:24 PM

If you have one try it out and report back. I still maintain that if it doesn't have the same internal vacuum passages as a late 94 it won't provide the correct advance signal. If the vacuum comes from below the throttle plates it is essentially manifold vacuum which will not give the proper signal. The 94 has 2 openings, one just above the throttle plates and the other at the venturi. These are connected by a passage in the carb body. The signal provided to the distributor is an amalgam of the vacuum at the 2 different openings, more from one or the other depending on throttle position versus engine load. Pure manifold vacuum would provide too strong a signal, ie: too much advance under normal road load or part-throttle operation. Under acceleration manifold vacuum drops off which would allow the retard springs in the distributor to retard the spark too much. When you think about it this system is rather ingenious and when in proper working order probably worked pretty well for a box stock engine.

03-23-2005, 01:24 PM	#2
Guest Posts: n/a	Re: 97 on a 49-53 engine- vac where?/doby/yoy mis If you have one try it out and report back. I still maintain that if it doesn't have the same internal vacuum passages as a late 94 it won't provide the correct advance signal. If the vacuum comes from below the throttle plates it is essentially manifold vacuum which will not give the proper signal. The 94 has 2 openings, one just above the throttle plates and the other at the venturi. These are connected by a passage in the carb body. The signal provided to the distributor is an amalgam of the vacuum at the 2 different openings, more from one or the other depending on throttle position versus engine load. Pure manifold vacuum would provide too strong a signal, ie: too much advance under normal road load or part-throttle operation. Under acceleration manifold vacuum drops off which would allow the retard springs in the distributor to retard the spark too much. When you think about it this system is rather ingenious and when in proper working order probably worked pretty well for a box stock engine.