Miata Mailing List: January 1996, Message #71
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   From: MattMiata@aol.com
Subject: Spark Plugs - was "Bad gas"
   Date: Tue, 2 Jan 1996 14:23:13 -0500

In a message dated January 2,  '95  Eric_Rowland@baynetworks.com (Eric
Rowland) writes:

>2)  Spark Plugs - The Mazda book gives three different heat options for
spark
>plugs.  I understand that I shouldn't use Splitfires, since they may run too
>hot on a 'charged car.  I'm currently running the NGK xxx6xx  plug,
installed
>by the dealer.  Should I run the coldest plug, assuming that the 'charger
>will keep things sufficiently hot?  (Convention says 'hot rodders' use
hotter
>plugs to get more power)

My car came from the factory with the BKR5E11 plugs. They looked fine at
10,000 mi. (6,000 km.) Timing was advanced to 14 degrees after checking the
plugs. I just pulled them out last week at 15,000 mi. (9,000 km.) and they
had signs of high speed glazing (shiny coating on the plug, in this case an
orange color.) According to a Chilton manual I have (general for all cars),
"During hard, fast acceleration, plug temperatures rise suddenly. Deposits
from normal combustion have no chance to fluff-off; instead they melt on the
insulator forming an electrically conductive coating which causes misfiring."
I had been experiencing a slight misfire condition for the last 600 miles or
so. I replaced them with the BKR6E11 plugs and the misfire went away. We'll
see if this cures the problem in the long run. BTW, the 14 deg. timing change
is the only mod to the engine (so far!)

I'm sure your SC's keeping the temp sufficiently high to run the BKR7E11
plugs. It seems the engine has no problem keeping things hot enough all on
its own.

Was the soot on the plugs black? How many miles are on them?

Hope this helps!

Matt Hess
'95 Classic Red R
Harrisburg, PA

P.S. - As for your bad gas problems, it seems like it can take forever until
it works itself out. I had a bad gas problem once this past summer; I think
it took something like 3 or 4 tanks full until it stopped.

"I like these cold, gray winter days.
     Days like these let you savor a bad mood."
	Calvin - from The Indispensable Calvin & Hobbes