Does anyone know what the dwell should be on a 250 6 cyl ?
I am not to sure what Dwell actually is ?
Is it the difference between the timing with the advance dissconnected and when it is connected ?
Dwell is the time the ignition points are closed measured in degrees. The point gap on the Chevy 6 is .019". This can be confirmed with a dwell meter, if the dwell is between 31-34 degrees, the point gap will be .019 on average. Point gap can affect ignition timing so dwell should be set before timing. When checking/adjusting ignition timing you want the vacuum advance disconnected to make sure the base timing is not affected by vacuum, and the engine idling low so the mechanical advance is inactive. The internal mechanical advance will advance ignition timing as engine speed increases and can be checked/measured with a timing light. The vacuum advance is a fuel economy function and advances ignition timing independantly of the mechanical advance. Under high load/low vacuum conditions such as accelerating, the vacuum advance tends to be inactive. Under low load/high vacuum conditions such as cruising, the vacuum advance tends to be highly active. Vacuum gauges were often refered to as economy gauges.
