forsmans@thequest.net wrote:

Paul,

As Ed Anderson mentioned plugs as a possible culprit for his rough
running 13b something from the past came to mind. Because of its high
compression and subsequent octane requirements I double-plugged the
heads on my BMW R100S years ago.  This enables me to use the lower
octane fuels we are stuck with today without having to retard the
timing.  The second plugs had a shorter reach and I could not get
platinum plugs in that size so I installed ordinary plugs there.
Platinums on top, regular on bottom (its a flat, opposed two
cylinder).

Since this is an older engine that was designed for leaded fuels I
sometimes will run a tank of 100ll just to keep the valves happy.
After a while the engine began to detonate badly under even a light
load using regular mogas.  Upon examination I found the electrode of
the platinum plugs was eaten away.  The engine was running only on
the single lower plugs, hence the detonation.

This leads me to question whether it is wise to use lead and platinum
together.  100ll may very well eat your platinum plugs for lunch.  I
don't want to get into the chemistry of it all, but gold amalgamates
in lead, as well a mercury.  Might not platinum do likewise?

Ed, are you using platinum plugs and 100ll gas?

Don Forsman

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