When setting ignition timing, how does having the vacuum hose connected to the distributor affect it?

Question

I have car with a 390 ford engine. I attempted to set the total timing at 36 degrees with a timing light. I did this without disconnecting any vacuum lines. Just hooked up the wires on the light, revved it up till it didn't advance any more and adjusted the distributor. I don't know much about this stuff. Is my timing set correctly or not?

Answer 1

You are not doing it correctly. There is a mark on the flywheel which you hi light with chalk, with the engine idling, you rotate the distributor until the pointer is over the white mark, or a few degrees to one side or the other, depending on how you want the engine to perform. You don't disconnect any vacuum lines when you do this.

Answer 2

the vacuum advance should be disconnected and blocked before you make that adjustment. it will advance timing when vacuum drops. you need ot go back and reset the timing.

Answer 3

Hi, there are two different things that advance the timing in the distributor. There is centrifugal advance which will advance the timing as the rpms go up there is also a vacuum advance that advances the timing as the vacuum  increases.  That is why you want to remove the vacuum line and time the car while idling.  I hope this helps.

Answer 4

You are generally supposed to set the timing with the vacuum advance blocked off, setting the timing with it hooked up could affect preformance especially at low speed acceleration.....