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View Full Version : How do you set timing? Vacuum hooked or not?


Fireball
10-25-2013, 07:30 AM
I'm used to set the timing with vacuum disconnected from distributor. Now my Ford made me wondering if this is the right method on our cars also? There seems to be at least 10 degrees difference on the balancer mark with/without vacuum at 500 rpm idle. Is this normal?

Distributor turns counterclockwise and motor clockwise when looked from front. My balancer has marks from TDC to 20 BTDC in 2dgr steps from left to right, and the marker on the block side is there. So I had too much advance at idle vacuum hose disconnected. To me it meant turn the distributor counterclockwise to retard advance. And what happened, I got even more advance! So I needed to turn my distributor clockwise, against it's rotation to retard timing. Something does not make any sense to me now.

Anyhow I set it to 6 degrees BTDC, but when I connect the carb vacuum it jumps to 22 BTDC. It idles OK but this bothers me. I'm running Pertronix II yet to my understanding it shouldnt play any role on this.

jopizz
10-25-2013, 08:40 AM
Yes, the timing has to be set with the vacuum advance disconnected. I'm not sure exactly how much advance there is at 500 rpm although 10 sounds like a bit much. The spec calls for a maximum of 12 1/2 at 1000 rpm. There is also some centrifugal advance that kicks in at 500 rpm.

It should be counterclockwise to retard timing as you mentioned. I can't explain why yours seems the opposite although maybe you're confusing how it's done. If you were originally at 0 degrees you have to advance it or turn it clockwise to get it to 6 BTDC.

John

Fireball
10-25-2013, 09:08 AM
Thanks for the confirmation of the vacuum John. The following tech bullet confirms my numbers are "normal". I still need more cigar and beer to figure out why my distributor had to be turned that way. Anyhow my timing was off and is now spot on.;)

"At idle, the engine needs additional spark advance in order to fire that lean, diluted mixture earlier in order to develop maximum cylinder pressure at the proper point, so the vacuum advance can (connected to manifold vacuum, not "ported" vacuum - more on that aberration later) is activated by the high manifold vacuum, and adds about 15 degrees of spark advance, on top of the initial static timing setting (i.e., if your static timing is at 10 degrees, at idle it's actually around 25 degrees with the vacuum advance connected)".

Fireball
10-25-2013, 10:07 AM
BINGO! So afterall my timing was retarded (and so am I). As John said I was still thinking it backwards on the balancer :p

Case closed.