You write:
> That thread on compression testing really confused me. I never
> lift off the oil damper caps on the carbs when I do compression
> tests. Is that was was meant or did I misread it?
I, too, found the initial post confusing. I have since come to
understand that what is desired in the compression test is to allow the
cylinders to get all the air that they need. (Of course, I'm the one
who just did a compression test without doing anything to allow the
carbs to get more air...)
What I present below has been collected from a couple of responses (if
this is wrong, correct me...). The general consensus is that when
doing the compression test, you want air to flow freely through the
carb so that lack of air isn't distorting the compression test results.
Thus, here is what one should do:
1) when cranking the engine, mash the pedal to the floor to
completely open the throttle butterfly valve.
2) lift the air valves within the carburetor. This would be
done by taking off the air cleaner, lifting the air valve,
and somehow holding it there. However, if you decide to
wedge anything in the carb to hold it there, be *extremely*
sure that it won't get pulled into the engine...
3) if you don't want to go to the bother of (2), a simpler
almost-as-good solution is to remove the carburetor damper
caps. Why does this help? Well, the purpose of the
carburetor damper assembly is to allow the air valve to
drop with little resistance, but to provide uniform
resistance against the air valve rising (to rise
slowly when more air is needed, so as to provide a rich
mixture under acceleration). In a compression test, this
would limit the amount of air getting to the
cylinders. When the carburetor damper assembly is removed
the air valve moves upwards more easily. (Although
gravity and the air valve spring are still forcing it
down.) As a test, try pushing the air valve up with the
damper assemblies on, and then with them off next time
you have the air cleaner off...
It's amazing how much there is to learn about these cars! What a great
hobby/pastime!
--ken
Kenneth B. Streeter | ARPA: streeter@sanders.com
Lockheed Sanders | UUCP: ...!uunet!sanders.com!streeter
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