Vacuum advance question

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Apr 4, 2003 | 11:44 PM

#21

Vetterodder

Safety Car

Joined: Feb 1999

Posts: 3,631

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From: Fountain Hills AZ

Re: Vacuum advance question (hudman)

Quote:

Could the timing be advancing too much at idle causing the poor idle?

Basically, the car would not run unless I stepped the idle up to 1200-1500 RPM or so.

Unless you go way too far with it, more advance at idle will result in a smoother idle. It will, by increasing torque, cause the idle speed to increase and require a carb adjustment to get it back down where you want it. Looking at it from another way, too little advance will require a higher idle speed in order to provide enough torque to keep the engine running.

Under hard accelleration, vacuum advance does not function and therefore will have no effect. Under light accelleration though, it is still partially contributing to advance and can increase throttle response under those conditions. Past idle, ported and manifold vacuum advance function the same. Ported advance was introduced as an emissions device and that remains as it's only benefit.

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