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JFairman JFairman is offline
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Join Date: Jul 2006
Location: S. Florida
Posts: 7,129
If you rev the motor up from idle quickly or "blip" the throttle the rpms will drop down a little below the regular idle speed for a second or two and then come back up to regular idle speed if it's running too rich.

It may also oscillate up and down at idle speed like Brian said. That's probably a negative side effect of the slow response time of mechanical air flow meter controlled fuel injection when it's running too rich at idle. Advancing the idle ignition timing can help clear up some of the running too rich at idle oscillation stuff if it does that.

When I had one it idled smoothest around 12.8:1 AFR and up to around 13.5 was fine too but 12.8 to 12.9 was the best with todays E10 93 octane unleaded gas.

Some of the problem is because of the ~E10 premium unleaded pump gas we get these days. Years ago gasoline had no ethanol in it.

Ethanol has oxygen molecules in it if that's the right word for it so the higher the percentage of ethanol to gasoline you're burning the richer the AFR mixture has to be because of the oxygen in the ethanol.. for it to run right.
Old 07-24-2017, 06:40 PM
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