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T77911S T77911S is offline
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Join Date: Oct 2006
Location: MYR S.C.
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Quote:
Originally Posted by JFairman View Post
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.
that's how I use to set the mixture on the 77s, just lean of blipping the throttle and surging.
the 930 idle drops down fine, no surging.
this really bugs me why it reads 11 but idles good. I want to know why.
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Old 07-25-2017, 04:47 AM
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