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| | | | Joined: Dec 2002 Posts: 127 Wrench Fetcher | | Wrench Fetcher Joined: Dec 2002 Posts: 127 | How can I tell if my vacuum advance is bad without a vacuum pump. It moves maybe 1/16 - 1/4 inch when throttle is hit. How far is it supposed to advance? Maybe mine is bad? Thanks! | | | | | Joined: Aug 2011 Posts: 835 Shop Shark | | Shop Shark Joined: Aug 2011 Posts: 835 | Should turn more than that. If you grab the distributor and give it a twist with your hand you can see about how far it will go. If you cant turn the distributor, something is wrong.You can also hook up a (clean!)rubber tube to the advance and suck on it, and you should be able to tell if the diaphram is busted in the advance.
Kurt | | | | | Joined: Dec 2002 Posts: 127 Wrench Fetcher | | Wrench Fetcher Joined: Dec 2002 Posts: 127 | I can turn the distributor by hand quite a bit, I will have to try the rubber tube too. | | | | | Joined: Feb 2002 Posts: 12,029 Cruising in the Passing Lane | | Cruising in the Passing Lane Joined: Feb 2002 Posts: 12,029 | if it moves it's not "bad" [which would be a shot diaphragm], but things might be gummed up dirty and you may be losing some vacuum to leaks, so it may not be responding "normally" ... the vacuum advance doesn't move the distributor it's full range of travel, it's simply to give a shot of advance while the revs come up and the centrifugal advance inside gets moving .... are you having problems with the way it runs?
Bill | | | | | Joined: Dec 2002 Posts: 127 Wrench Fetcher | | Wrench Fetcher Joined: Dec 2002 Posts: 127 | Yeah, I am having problems with a backfire on deceleration through tailpipe. | | | | | Joined: Feb 2002 Posts: 12,029 Cruising in the Passing Lane | | Cruising in the Passing Lane Joined: Feb 2002 Posts: 12,029 | more likely a fuel supply problem, not ignition - check plugs for rich running, check compression, check valve adjustment
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