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Old 06-18-2013, 12:07 PM   #6
domeier
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Join Date: Sep 2011
Location: San Jose, California
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Re: diagnosing this fuel/spark issue

Quote:
Originally Posted by BiggSixx1970 View Post
...but I thought that if the vacuum advance was acting up it would idle correctly, but run rougher or cut out as the rpm's increase?... If memory serves me correct, when I replaced my distributor last summer, to set my idle timing I set it without my vacuum advance connected, meaning the engine should idle without the advance, just cut out as the rpms increase, right?
Vacuum leak will cause it to idle rough or not idle at all. When you adjust ignition timing or idle mixture, the vacuum advance diaphragm needs to be disconnected *and* plugged off at the manifold/carb.

Think about it this way: The engine needs a particular mixture ratio of fuel and air to run, so if you have a leak in your vac system, you're sucking in additional air and making the mixture too lean. It'll be farty, poppy, rough or no idle.

Or... maybe your distributor hold-down clamp loosened up and allowed the ignition timing to change?
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