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Hey all, Did my timing today, set it to 10deg at idle (Vac adv. unplugged). But with my vacuum advance plugged in after I set the timing to 10deg, my timing goes through the roof as I accelerate! At 1500RPM its at about 30deg, and keeps going! Off the charts (Or balancer).

But if I unplug the vac. advance, it goes about right, at about 2000 it reads 25deg.

Any ideas why my vacuum advance distributor decided to become a mechanical? :D

Thanks

Chris
 

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Contributing Sr Motorhead
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5,470 Posts
Distributor advance

Any vacuum advance distributor will also have a mechanical advance. That's the weights and springs are for you see down there inside the distributor! By adjusting the wights and varying the springs you can change the rate of timing advance.

Most V-8 engines want about 34-38 degrees of total advance at higher RPMs. A straight mechanical advance will give a linear advance 'curve' while the vacuum lets you have a more tunable curve.

If you get ahold of a 'advance' timing light, you just dial in the total advance you want and then look at the timing mark. IE, if you dial in 36 degrees total advance into the light, and then you put the light on the car while running at 3000+ rpm, the light will fire when you see 0 degrees on the pointer. This makes adjusting the total timing much easier since you have all of those marks on the balancer at around 0 degrees.
 
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