vacuum advance
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New User
Joined: Oct 1999
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vacuum advance
I have a 390 and need to know whether to hook the vacuum advance to the carb or to the manifold. I read somewhere that you hook it to the manifold but how does that advance it when vacuum decreases as you push the throttle?
Senior User
Joined: Jun 1999
Posts: 103
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From: Palo Alto, CA
vacuum advance
If your diaphragm has one port, hook it to the carb. If it has two, hook the one closest to the distributor to the manifold and the other one to the carb.
I strongly recommend that you pull the cap off and make sure that both mechanical and vacuum advance mechanisms work freely. Mine were all gummed up and caused the truck to run like crap.
To check the vacuum advance, rotate the plate that has the points or sensor towards the diphragm.
To check the mechanical advance, grab the rotor and rotate it away from the diaphragm and make sure it springs all the way back. It should rotate only a few degrees.
If either of these don't operate smoothly and freely, rebuild the distributor. It's fairly easy. If you want help, email me and I'll tell you how.
Also make sure the diaphragm doesn't leak.
I strongly recommend that you pull the cap off and make sure that both mechanical and vacuum advance mechanisms work freely. Mine were all gummed up and caused the truck to run like crap.
To check the vacuum advance, rotate the plate that has the points or sensor towards the diphragm.
To check the mechanical advance, grab the rotor and rotate it away from the diaphragm and make sure it springs all the way back. It should rotate only a few degrees.
If either of these don't operate smoothly and freely, rebuild the distributor. It's fairly easy. If you want help, email me and I'll tell you how.
Also make sure the diaphragm doesn't leak.
