Vaccum Advance

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Nov 15, 2005 | 07:34 PM

workingdog

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Vaccum Advance

We been having a hard time getting our recently rebuilt 390 to run smoothly in our '68 F250 until we disconnected the vaccum advance. Now it idles and revs great. Any idea what that indicates?

Petre

Nov 15, 2005 | 07:45 PM

fordraceboy

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a hole in the vacuum can creating a vacuum leak... first guess..

Nov 15, 2005 | 07:45 PM

Bear 45/70

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From: Union, Washington

Where was the vacuum advance hose connected to? It sounds like you were connected to manifold vacuum instead of carb ported vacuum.

Nov 15, 2005 | 07:47 PM

ford390gashog

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From: Brentwood,CA

do you have the vacuum line running to a ported vacuum? because the vac advance won't affect it at idle.

Nov 15, 2005 | 07:51 PM

workingdog

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It's definatley not connected to the manifold, but we may have it connected to the wrong outlet on the carb.

Nov 15, 2005 | 07:52 PM

ford390gashog

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yep probably. base timing should be 12 btdc.

Nov 15, 2005 | 08:30 PM

fordeverpower

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From: iowa

workingdog, the carb has a manifold port and a ported port. The manifold port is below the throttle blades and the ported is above them.

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Nov 15, 2005 | 09:51 PM

workingdog

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No, the engine starts to stall.

Peter

Nov 15, 2005 | 09:56 PM

#10

ford390gashog

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are you sure you have the timing and mixture set right?

Nov 15, 2005 | 10:00 PM

#11

Bear 45/70

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From: Union, Washington

By stall I assume (very bad thing to do) that you mean the rpm drop off and the ingine splows down. Is this a dual diapham advance unit with 2 nipples on it? Is the vacuumat idle on the port you are connection the hose to on the carb?

Nov 16, 2005 | 03:03 PM

#12

workingdog

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So we got the basic timing done (it was OK to begin with) and the mixture and idle set roughly and we got the vacum line connected to the right port on the carb so it does not effect idle. When we rev the engine with out the vacum advance connected it runs great, when we connect the vacum advance it stumbles when we rev it. Is my vacume advance bad? Can I just leave it disconnected?

Nov 16, 2005 | 05:07 PM

#13

krewat

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From: Long Island USA

Is this thing points? Almost sounds like the upper bushing is shot, and the vacuum advance pulling the plate around is sending the dwell out the window.

Or if it's a Duraspark, you have a broken wire to the pickup.