Fuel flow at idle

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CpnCrunch
Posts: 53
Joined: Thu Jan 16, 2020 3:59 am

I just noticed today that my fuel flow (O-360) is 2.5gph at 500rpm idle, but only 1.5gph or less at 900rpm. The same thing happens when leaned or not, or when stationary or taxiing (it just uses a little more than 2.5 when not leaned). Looking at how a carb works, I'm guessing it's just the horrendous inefficiency of the idle jet on the carb. Is that why spark plug fouling is such a problem when idling?


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Liquid_Charlie
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Location: Sioux Lookout On.
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If the engine seems normal it's got to be gauge related.
"black air has no lift - extra fuel has no weight"
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Slick Goodlin
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Joined: Thu Jan 16, 2020 3:24 am

Fuel flow in a small piston (and hell, maybe everything) is derived somehow from pressure, right? Could it be that at idle your system is seeing the equivalent pressure of a 2.5 GPH flow?
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CpnCrunch
Posts: 53
Joined: Thu Jan 16, 2020 3:59 am

It's a JPI 450. As far as I know it has a little paddle wheel in the fuel line. It seems accurate the rest of the time, so I don't see why it should be reading a bad fuel flow at idle. Engine runs perfectly normally at idle.
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