At 08:55 PM 5/10/2005 -0400, Tim Benner wrote:
>The pistons are not binding... both raise and fall freely when i move their
>respective throttle arms. The front one falls to the bridge when the car is
>not running. The timing was OK before I started with the carbs. Could the
>extra vacuum form the now not leaking shafts be affecting the timing so that
>it idles fast? Compression was good last time I tested... within 5 lbs.
See if any of the various vent holes are blocked, possibly by a gasket being
installed backwards.
You can also do a leakdown test of the piston assembly:
Remove the air chamber and piston, and remove the spring and damper.
Plug the two holes in the bottom of the piston with Play-Doh, etc.
Hold the assembly upside down, lift the piston up, and see how long
it takes to sink down into the chamber as the air inside leaks out through
the gap between the edge of the piston and the chamber wall.
It should take several seconds. If it plops right down, then air is leaking
someplace,
and the piston won't be able to be raised properly when the engine is running.
Do this test on both carbs, and compare the results.
You could also try temporarily swapping the chamber/piston/needle assemblies to
see if the problem switches to the other carb.
Finally, be sure that the needles are centered in the jets and not jamming
the pistons at idle. Jet centering is a bit tricky. It helps a lot to always
replace the thin, crushable aluminum washers inside the jet holder assemblies.
Order a dozen, so you never run out.
Doug Braun
'72 Spit
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