Vaccum advance
Tech Contributor
Joined: Aug 1999
Posts: 14,380
Likes: 6,390
From: At my Bar drinking and wrenching in Lafayette Colorado
Put a long hose on it and suck on it. You should be able to make the advance move by sucking on the hose. If it will not hold a vacuum, you need to replace it.
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
Its right at idle if you have the hose on "ported" vacuum.If you have the hose on "manifold" vacuum and it makes no difference the vac. can is probably bad or make sure the breaker plate is not locked up due to too long of points or cond. screws.
Drifting
Joined: Dec 2002
Posts: 1,946
Likes: 28
From: Long Beach CA
Pull the hose off the vacuum advance with the engine idling and put your fingertip over the end of the hose. If it's trying to suck in your fingertip, it's running on manifold vacuum and you have a problem with the vacuum advance. If you don't feel any suction, then it's running on ported vacuum and your vacuum advance is most likely OK. You can leave it that way, or redo things to run it off manifold vacuum.
Safety Car
Joined: Jun 2004
Posts: 4,652
Likes: 80
From: Lakeland Florida
You can also take your distributor cap off and visually check if this is moving. Even though you can connect a hose to the end and suck on it to create a vacuum, there may still be an issue with the extension rod that connects t the advance plate. By removing the cap, then sucking on the end of the hose connected to the advance unit you shouuld be able to see the rod pulling or moving the advance plate on the distributor.
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