ROP masking of engine problems

"Roger Long" wrote
Early in the spring, Walter Atkinson of Advanced Pilot Seminars, posted
somewhere that any engine that was conforming and without induction leaks,
ought to be able to run at the optimum (for a simple engine) 25 degree LOP
spot.

That's way too broad. Some engines simply have poor fuel/air
distribution, and will never run LOP until this is fixed. That's how
GAMI makes money - bandaiding poorly designed engines so that they are
somewhat less poorly designed. That's not a slam on GAMI, BTW - they
do as much as the FAA will let them do.

However, the small 4-cylinder Lycomings have very good fuel/air
distribution, and run LOP just fine stock - assuming, of course, there
are not other problems such as bad plugs, intake leaks, clogged
injectors, injector line leaks, etc.

I run my IO-320's LOP routinely. I've had the plane well over 700
hours, the engines have 1500 hours and 14 years on them, and I have
changed one jug. In fact, the compressions were all over the place
when I bought the plane, and operating this way brought them up to 78
or better on ALL cylinders and kept them that way until long past the
1000 hour mark. And every time I failed to get smooth operation well
LOP, it was an indication of a problem that I was able to catch early.

I had always assumed that fuel injection was a must for this, but upon
reflection this is just stupid. As long as the carb does a good job
of atomizing/vaporizing the fuel, it should not matter. That would
explain why carb heat makes a difference, though - hotter air means
more complete vaporization.

So basically, I agree with your premise - just understand that it
won't work for EVERY make and model engine/induction system
combination. Clearly works for yours, though.

Michael

(Michael) wrote in
om:

I had always assumed that fuel injection was a must for this, but upon
reflection this is just stupid. As long as the carb does a good job
of atomizing/vaporizing the fuel, it should not matter. That would
explain why carb heat makes a difference, though - hotter air means
more complete vaporization.

Absolutely... it's all about the Fuel/Air ratio. How you get it the same
to all cylinders is unimportant.

Now, having said that, most carb systems do such a poor job of it that it
is actually TAUGHT to primary students as a leaning method. "Just pull
that little red knob until the engine runs rough, then push it back in a
little."

As you surmise, every now and then, you get a carb'd engine that runs very
smoothly, even very lean of peak. I've seen more than one newly minted CFI
get surprised when he goes to show the student how to lean... and the
engine just quietly and with no muss or fuss - QUITS!

jmk