At 12:00 PM 5/3/2001 -0400, Joe Short wrote:
>Brent wrote
>>Also running the engine a tad on the rich side might help the pinging and
run-on but probably will sacrifice some economy and emissions.
>
>Be carefule about how rich you get. You don't want to wash down the
cylinders. The DPO had done this on my car, the end result was piston slap
so bad it sounded like a rod knock. The only fix was to rebuild the engine
and overbore the cylinders.
This effect would probably require an awful lot of excess fuel, in which
case it may well thin the oil in the crankcase and lead to bearing failure
first.
But there is another problem with overly rich mixture. On occasion I have
had one carb adjusted two or three turns rich and left that way for a few
thousand miles of driving. This can result in heavy carbon deposits in the
combustion chamber, such that the piston rings can hang up in the grooves
causing significant loss of compression, and also blow-by into the
crankcase which can result in oil loss through breathers or external oil
leakage. It can also cause carbon deposits on the valve seats to the point
of leading to valve leakage, which can cause loss of compression and
ultimately severe burning of the exhaust valves by erosion.
I am told that for a high compression (and maybe slightly tempramental)
race engine that you want to run it somewhere between slightly rich and
flooded, but never lean. Running a hot engine on the lean side can
actually burn aluminum pistons.
Barney Gaylord
1958 MGA with an attitude
http://www.ntsource.com/~barneymg
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