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Old 09-29-2018, 06:35 PM   #5
geezer#99
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Join Date: Aug 2009
Location: Bowser
Posts: 10,001
Re: Motor goes from lean to rich at idle.

Intake is cold when it goes rich!
The fuel vapour goes from fine mist to heavier fuel droplets (liquidizes).Heavier fuel doesn’t burn well and goes out the exhaust. Shows rich on your analyzer.
When your intake is hot the fuel vapour stays normal.

Try this test.
When it goes rich shut off the motor for 5 minutes. The intake should warm up from heat soak in the motor. Hot air rises and heats the intake plenum. Should stay lean then.
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