VMAZDA@aol.com wrote:

About the firing of the plugs on the 13B 1986 and up was changed from earlier
years because of the use of the computer. Earlier years had a dist. so every
plug had to fire independently but when the 86 came out MAZDA found it easier
to fire both leading plugs at the same time. One leading plug would fire on
the rotor with compression and the other leading plug would fire in what we
call a dead hole or in the exhaust cycle. When it came to the trailing plugs
this could not be done because if you fired the second trailing plug at the
same time as the first you would be firing into the intake cycle of the second
rotor. Bad idea. That is why the leading plugs fire more often. Why was this
done? Because the engine is a polluter. MAZDA wanted to make sure that the
leading plugs stayed clean. The engine could pass emission standards with the
trailing plugs fouled out but not the leading. I know because I was there.
VMAZDA

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