The fuel system must be vented, air has to get into the
tanks and the carb float bowl. Your fuel tanks are probably
OK since they do feed fuel and the tank has not collapsed.
Fuel flows out the carb jet due to differential pressure
between the venturi and the float bowl in a ratio determined
by the float setting which controls the fuel level in the
bowl.
Retarding the throttle drops the MAP (your Piper does not
have a MP gauge) and raises the pressure (decreases the
venturi effect) at the jet. This can cause a stumble,
particularly if the fuel level is not at the proper level
due to a float out of adjustment or a problem with venting.
When you retard the throttle rapidly, you can "detune"
engines with dynamic counter-balanced crankshafts (not on
your Piper model) and cause other effects on the prop and
other parts, such as alternator belts. But advancing the
throttle too fast can cause a hesitation if the carb does
not have an accelerator pump circuit to increase the fuel
flow for acceleration before the air-flow stabilizes.

If I was flying your airplane, I'd do a visual inspection of
the carb looking for fuel stains that might indicate a fuel
or air leak. At the next 100 hr/annual, I'd consider
dropping the float bowl and checking the float.


--
James H. Macklin
ATP,CFI,A&P



"Dave" wrote in message
...
| Hmmmm... OK..
|
| Could you elaborate?
|
| I think I see where you are thinking, deceleration if the
| aircraft speed or engine rpm?
|
| Suddenly closing the throttle would cause the mix to go
lean?
| - if the carb vent were plugged?
|
| Thinking...
|
| D
|
|
| if On Sun, 4 Dec 2005 19:52:28 -0600, "Jim Macklin"
| wrote:
|
| float level and carb vent.
|