In a message dated 8/7/03 2:11:25 PM Eastern Daylight Time, frank@zk3.dec.com
writes:
<< What causes it? There are two kinds I guess: either in the intake, or
the exhaust. >>
>From the exhaust: rich mixture ( usually on coast ) ,add some air either
from a leak or the rich mixture making it's way up the tail pipe= boom.
>From the intake: Lean mixture at cold start or lean spot while accelerating.
Lean mixtures are hard to light* and burn slowly/eraticaly when lit. When
the piston is coming up on the exhaust stroke, the fuel is still burning, the
intake valve opens and the intake goes boom. This slow burn is also hot so it
causes engines to run hot dumping heat into the exhaust ports ( and cooling
system ).
If the distributor cap is wet, the spark will occur at any time. If a valve
it open, that end can go boom.
* The 75 Honda CIVIC with the CCVC engine used a small ( 1/4" ) intake valve
attached to a rich carburetor. The normal intake valve was attached to a carb
running a lean mixture. The rich mixture was directed to a small chamber (
like a diesel with a pre cup) containing the spark plug. This rich mixture lit
the lean mixture in the main cylinder.
The Chrysler/ Mitsubishi 2.6 4 cylinder from 81 to 88 ( except vans) used
the same system called MCA jet.
Harold
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