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post #1 of 3 (permalink) Old 06-18-2009, 09:07 PM Thread Starter
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460 timing issue

On my stock 1979 ford f250 with a 460, the sticker shows the motor should have 14*BTDC timing. On the factory Holley/Motorcraft carb, the vacuum advance was plugged into the the only vacuum port on the carb which was below the throttle plates. If this setup was right, then that means the motor should have vacuum advance at idle? After I installed the Edelbrock 1406 carb, and plugged the advance into ported vacuum (which is what edelbrock reccomended) with the timing set at 14*, the motor did not idle near as well as with the timing set at 14* and plugged into full manifold vacuum at idle (the idle quality was rough and sloppy even after tuning). Is it OK to run the motor with the full manifold vacuum at idle? This does give me like 28* advance at idle though. Any suggestions would be greatly appreciated. Thanks in advance!
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post #2 of 3 (permalink) Old 06-21-2009, 11:49 AM
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Two different thoughts here for two different issues. I have run manifold vacuum for advance on a handful of vehicles. I've done this for optimal around town and highway cruise fuel economy (lots of advance at and just off idle is great for trail riding fuel economy). With any performance driving manifold vacuum drops off quickly as the throttle is opened. This can work well for heavier load applications as well, open teh throttle a lot to get a heavier vehicle/load moving and your vacuum advance drops sharply off, once up to speed and off the throttle vacuum advance comes back in for an increase in fuel economy.

Put a vacuum gauge in the car, ideally two vacuum gauges, one to manifold one to ported. Watch how they react in comparison to the other. Also get an adjustable vacuum advance can as you will want to limit how quickly vacuum advance comes in depending on the engine/vehicle/and which vacuum source you use. One thing though, regardless of which vacuum source I use I will always get my machanical curve set how I want it first. Vacuum advance is not a band aid, it is simply "extra" timing to help with fuel economy if the application will tolerate extra timing at part throttle or cruise.
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post #3 of 3 (permalink) Old 06-21-2009, 12:50 PM
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As I understand it, when setting timing, it needs to be done with the vacuum advance DISCONNECTED. When connecting vacuum advance afterwards advance will increase indeed that's normal.
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