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911 1974 erratic idle


Vehicle Information: Model: 911; Year: 1974; Body Type: Coupe; Total Mileage: 106,000;

This is not a question, but a solution to the erratic idle conditions I have been experiencing with this 911. I checked all of the usual fixes on this website to no avail. What I finally found was the vacuum advance,( retard ) plate in the distributor was very sticky and not freely moving. During idle, the manifold vacuum is high and this actually retards the timing 6 degrees during idle. When I first started the car, in the idle position the idle speed was 1100 rpm as it's supposed to be. Blip the throttle once and the vacuum drops and the vacuum retard advances 6 degrees and sticks there. When the throttle is at idle position the timing is 6 degrees btdc raising the idle speed 7 to 800 rpm. The mechanical advance is easy to check out through the window covered by the plastic plug but the vacuum advance plate is staked in place and cannot be removed easily. I was able to spray solvent from the inspection holes and also to drop some oil on the bearing and work the plate back and forth. I now have much better idling. Maybe you folks have a way to remove the breaker plate where it would be easier to service. I checked the vacuum diaghram and its spring and they were ok. There is a notch on the actuating arm from the diaghram that limits the total advance to 6 degrees, at the crankshaft,thats why you set the timing with the vacuum hose connected. I first spotted this when I would remove the hose and the timing wouldn't always change. Sometimes yes and sometimes no.Best Regards, George Blessing

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