This is why we do runups

Jim,

Yes, but that statement should be further qualified by saying that descents
should be made at less than 75% power or else EGT and CHT could exceed
operating limits. 65% power sounds like a good number. Some carbed engines
with good fuel distribution will run smooth when too lean (close to peak,
either rich or lean of peak).

Actually, that doesn't make sense. I think you may mean
"inappropriately" lean, rather than too lean. The worst spot is about
50 degrees rich of peak when at high power as that is generally max
for CHT and BMEP. So long as you are richer or leaner than that, you
aren't going to hurt the engine. Leaner is generally better in terms
of keeping temps down and plugs from fouling, so long as the engine
runs smoothly.

All the best,
Rick

"Rick Durden" wrote in message
...
Jim,

Yes, but that statement should be further qualified by saying that
descents
should be made at less than 75% power or else EGT and CHT could exceed
operating limits. 65% power sounds like a good number. Some carbed
engines
with good fuel distribution will run smooth when too lean (close to
peak,
either rich or lean of peak).

Actually, that doesn't make sense. I think you may mean
"inappropriately" lean, rather than too lean. The worst spot is about
50 degrees rich of peak when at high power as that is generally max
for CHT and BMEP. So long as you are richer or leaner than that, you
aren't going to hurt the engine. Leaner is generally better in terms
of keeping temps down and plugs from fouling, so long as the engine
runs smoothly.

Yup. I did not explain it very well.

David Megginson wrote in message ...
Chris Kennedy writes:


Up here in the mountains we lean to the point of stumbling and try not
to reduce RPMs below 1200 on our O-540 (as does the local FBO with its
O-360). Except on very cold winter days we lean for departure as
well.

As far as I understand, carbureted engines have a separate idle
mixture control that needs to be adjusted with a screwdriver on the
carburetor itself (i.e. on the ground, by an A&P). If that is set too
rich, you can lean during ground idle until the cows come home and
still end up with fouled plugs.

From Chris's description, he's leaning to just above idle cutoff.
That will do the trick no matter how your idle mixture is set. On my
O-360, the mixture control is just above idle cutoff and the most rpms
I can make are about 1200. Leaning that aggresively guarantees that
you will not take off without enrichening the mixture.

John Galban=====N4BQ (PA28-180)

Dear John:

Mechanically and technically, and while I'm not doubting your post and your experience with plugs,
this makes no sense.

If plugs are cleaned and gapped there is just no cause attributable to plugs that would lead to extra
fouling. If, however, the plugs had worn to the level where the electrodes are spaced too far apart I
can see where the uneven spark would cause uneven combustion which, in turn, would cause lead
fouling.

I'm racking my brain to think where time in service would make a difference - and the only conclusion
is mechanical failure, possibly a cracked ceramic area of some type of wear, if other than the
electrode gap?

If you ever learn more for the reason I'd sure like to learn about it.

My experience has been that plugs will last until the electrode tips are worn and unreliable - and
this can be 1000 hours or more if the cylinders are in good shape. If I had to make a guess, I'd say
that while plugs may be well maintained, they can wear due to heat or lean of peak operation etc.,
and that this may shorten plug life.

Pat




John Galban wrote:

"Dan Luke" c172rgATbellsouthDOTnet wrote in message ...

Is your O-360 bad about fouling plugs? Mine's terrible - much worse than the
O-320s on the Skyhawks I used to fly. I have to be an absolute fiend about
leaning to keep my plugs clear.

It's not nearly as bad as my O-300 was when running 100LL. Overall,
it's not really a huge problem. If I forget to lean for a long taxi,
I stand about a 50/50 chance that I'll foul a plug. It's usually
minor fouling and clears up after about 10 seconds of leaning durning
the run up.

Over the years, I've noticed that the age of the plugs has an effect
on fouling. When the plugs start getting around 400 hrs on them,
they tend to foul easier.

John Galban=====N4BQ (PA280-180)

while plugs may be well maintained, they can wear due to heat
or lean of peak operation etc., and that this may shorten plug life.

Pat

Assuming your engine runs smooth when LOP, LOP operation should
increase plug life, not shorten it. Plug fowling will be much
less likely, and assuming you are operating far enough into the
LOP range, the cylinders and plugs will be running cooler.

~Paul

Pat Barry wrote in message ...
Dear John:

Mechanically and technically, and while I'm not doubting your post and your experience with plugs,
this makes no sense.

If plugs are cleaned and gapped there is just no cause attributable to plugs that would lead to extra
fouling. If, however, the plugs had worn to the level where the electrodes are spaced too far apart I
can see where the uneven spark would cause uneven combustion which, in turn, would cause lead
fouling.

I'm racking my brain to think where time in service would make a difference - and the only conclusion
is mechanical failure, possibly a cracked ceramic area of some type of wear, if other than the
electrode gap?

While I don't have any specific data, I've always assumed that it's
some type of wear. I generally get about 700 hrs. out of a set of
plugs. That's about the point where the electrodes start taking on a
football shape. When replaced with brand new plugs, I always noticed
that the propensity for fouling decreased. Upon reading your post, I
see you're point. As the plugs aged, one or more may have had some
sort of mechanical problem that caused a weaker spark (as evidenced by
the increased fouling).

John Galban=====N4BQ (PA28-180)