Re: Tom tuned his carb??!!

[jlandry@domain.elided (John A. Landry)]

The aliens commander decided Tom Mandera <tsm1@domain.elided> would make a
perfect specimen for dissection, and he yelled...

>Hmmm.. "idiot" Q... Something must be wrong tonight, I'm making sense of 
>so many things... the "rattle" that I've heard before and heard some more 
>tonight when I accelerate hard.. is not just a "rattle" but.. that's the 
>PING everyone's spoken about.. here I thought it was a rattle not a 
>ping.. ;-)  
>
>I'm running ~ 10 deg advance.. I also have about 16" of vacuum at 700rpm 
>idle..

Tom,

If you don't change anything else (like switching to premium fuel), my
experience has been that the pinging is best controlled by retarding your
timing a bit.  You might try 5 to 7.5 degrees BTDC instead of the 10
degrees you have now.

Changing your carb jetting by enrichening your air / fuel mixture will help
somewhat, but not nearly to such a great degree as the timing will.  If you
run a *really* lean air / fuel mixture you will certainly get pinging under
slight to moderate load conditions.  However, once the air / fuel mixture
is in the proper range, pinging is controlled to a greater degree by timing
(for a given fuel octane rating).

BTW, the vacuum an engine has at any given rpm and load is not very useful
for comparison purposes against other engines.  Each engine will have a
slightly different vacuum reading depending on not only where the vacuum
signal is taken, but things such as the camshaft, carburetor, air cleaner,
valve condition, transmission drag, etc.  If you notice a change over time
in your engine's vacuum reading, then it's worth investigating.

Regards,

John L.
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jlandry AT halcyon DOT com      | 
Conservative Libertarian        |  "The road to  tyranny, we must never
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Commercial Helicopter - Inst.   |                     William J. Clinton
http://www.halcyon.com/jlandry/ |    10-15-95, speech at the Univ. of CT