Fuel flow and leaning this time

"xerj" wrote in message
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I understand that roughly speaking increased power = increased fuel flow.
Therefore, it makes theoretical sense to me that as you pull the mixture
back and get closer to stoichiometric that you will see an increase in
fuel flow because the power output of the engine is increasing. What I
can't do is explain why mechanically.

Perhaps it's because that doesn't happen?

Most of the planes I've flown don't even have a fuel flow gauge. But the
ones that do have one, they show exactly what one would expect: as the
mixture is leaned, fuel flow decreases.

For example, with the TIO-540 in my airplane, flow flow readings are
roughly:

30 gph at full power, full rich
20 gph at cruise power, full rich
15 gph at cruise power, leaned to 50 degrees ROP

I do not see the fuel flow increase while leaning from full rich to 50
degrees ROP at cruise power. The fuel flow correlates directly to the
mixture control, and I do not see the fuel flow increase as mixture is
leaned. Ever.

Now, not that I've seen this personally, but I can imagine that a fuel flow
"meter" that is actually a fuel *pressure* meter might show you the behavior
you're seeing. Given Cessna's preference to label a low-voltage light as an
"overvoltage" light, I wouldn't be surprised to see some manufacturer
install a fuel pressure gauge but then call it a fuel flow meter. But I
have a hard time seeing how such a gauge would ever be able to show anything
approximating the actual fuel flow. That's not to say it couldn't...just to
say I'm not familiar with such a design, and so don't know how it would
work.

Pete