I put a CDI on the leading coil on my RX-7, to test it prior to
    possible installation on my Long-EZ. But I was wondering, if the lead
    deposit forms on the ceramic insulator and shorts out the plug, I don't
    think even CDI will prevent that? Maybe the only thing that can be done
    to minimize lead fouling is very aggressive leaning?*

    This is from the ngk website.

    Lead Fouling
    Lead fouling usually appears as yellowish brown deposits on the
    insulator nose. This can not be detected by a resistance tester at room
    temperature. Lead compounds combine at different temperatures. Those
    formed at 370-470°C (700-790°F) having the greatest influence on lead
    resistance.

    CDI system have the ability to fire through the lead for some
    strange reason. That is the main rational for using them.
    You probably missed reading the updated ACRE web site on
    ignition systems. Most of this data is from
    Heinz Heisler book Advanced Engine Technology.

    http://www.rotaryeng.net/Why-CDI-2.txt
    http://www.rotaryeng.net/AVAIL_SECOND_VOLT.GIF
    http://www.rotaryeng.net/2ND_VOLT_COMPAR.JPG

    Paul Lamar ...No rotor no motor.


I remember discussing it on the list but didn't know you put the info on
the website.
I bought a Crane HI-6 and installed it in my RX-7, very easy to
install, it is running on the leading coil only. I'll transplant it to
the Long-EZ soon. I suppose the CDI can bust the lead deposit by blowing
open the "short".


Here is some info from Lycoming, it implies that running a cooler plug
can help with some lead deposits:

Spark plugs should be rotated from top to bottom on a 50-hour basis, and
serviced on a 100-hour basis. If excessive spark plug lead fouling
occurs, the selection of a hotter plug from the approved list in Service
Instruction No. 1042 may be necessary. However, depending on the type of
lead deposit formed, a colder plug from the approved list may better
resolve the problem. Depending on the lead content of the fuel and the
type of operation, more frequent cleaning of the spark plugs may be
necessary. Where the majority of operation is at low power, such as
patrol, a hotter plug would be advantageous. If the majority of
operation is at high cruise power, a colder plug is recommended. Spark
plug fouling is not limited to engines that were certified for 80-octane
aviation fuel, but which are using the higher leaded 100-octane
gasoline. Therefore, the techniques recommended herein for operation and
maintenance apply to all Lycoming piston engines, but with emphasis on
the 80- octane engine using 100-octane fuel.

Perry Mick.

You sent a Crane pdf file Perry.
Where is the Lycoming data?

Paul Lamar


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