Tracy Crook wrote:

Anderson Ed wrote:

Tracy, I remember you mentioning that you had some rough running due to
spark plug deteriotation, did not recall that until after I left the
airport for home.  I did discover a couple of flights ago that I was
running way too rich >6000 rpm and had reduced the injector timing until
reducing the mixture control knob to lean would cause the engine to
change sound and EGT to go up.  I am now wondering if my leaning the
engine would have considerably shortened the life of the plugs.  I am
using single electrode plugs rather than the stock.

Any thoughts - I will pull the plugs this coming weekend, but thought I
would inquire as to any other possible causes before I tear into the
problem.

Ed Anderson
RV-6A N494BW.

I don't think leaning the mixture could have hurt the plugs but OTOH, I
don't know how the single electrode kind you are using would react.  Depends
on heat range etc.. If anything, the too rich mixture would more likely
cause a problem.  But why are you using those things?   I see no reason to
not use the standard Mazda specified plugs (4 electrode, horizontal gap)
(NGK brand is best).

The fact that the engine ran rough when cold (idle condition I assume?) and
improved when warm would seem to indicate that it was too lean when cold (or
the mixture is badly out of balance between rotors?)

You must have been REALLY too rich above 6000.  The fact that after you
reprogrammed for leaner above 6000 and the EGT still went up when you leaned
using the manual mixture control tells me you were still too rich.
Assuming there is a reasonable range on you mixture control, the EGT should
always go down at the bottom (lean) end of the adjustment.   I set mine up
so that peak EGT is at about center and it goes down on either side of this
setting.  In aviation use, you need a very wide range on this control.  Mine
gives a plus or minus 30% (fuel flow) range on the mixture control knob.

BTW,  except for Max performance take-offs and top speed tests, I always run
on the lean side of peak EGT.  Unless you REALLY need the power, running
anywhere on the rich side of peak EGT is throwing gas away for nothing.
Unlike piston engines, there is never the danger of burning a valve or
piston.  IMHO, When in doubt, LEAN IT!  The worst that can happen is the
power goes down if you go too far.   If the engine runs rough soon after you
lean below peak EGT it is an indication of un-even mixture distribution.  If
mixture is even, the engine will start dropping lots of RPM (but still run
smooth) long before a lean miss sets in.   This effect is so drastic that at
altitudes above 10500 I set WOT and actually adjust power using the mixture
control.  This gives the best BSFC under these conditions.  Can you adjust
the rotor mixtures independently on your EFI?  I found this to be a must
for getting best economy.

Keep us up to speed on how it goes Ed.

Oh, before I forget,  after that last trip to Copperstate, I found that my
ignition timing was too far advanced and the engine was on the edge of
detonation at full power. This was a factor in my sparkplug problems.
 Don't ask, I don't know how I did something that dumb.

Tracy Crook   rws@altavista.net

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