curious "cruise control" on my '57

[Philippe COURANT <accf_clb@xxxxxxxxxxxxxxxx>]

Hi,
Today the weather was fine so i made a short trip (40 miles) with
my '57. As i drive the car on straight road with few traffic, i
want to see if the car goes fast. So i put a heavy pressure on
the right pedal !! Speed increase fastly, 40, 50 , 60 mph but at
65 mph a curious thing appears: the engine suddently slows down
until speed return to 60 mph. The same feeling as if i've
released a little the gas pedal... Then (as i don't release the
pedal) the speed increases again until 65 mph then slows down,
then increases etc.. The gas pedal was not on the floor but there
was no effect if i pushed it to floor, no engine rev.
modification, like an automatic (and non adjustable !) cruise
control !!
I release the pedal until speed slows to 55 mph then i smash the
pedal to floor: the car rushs very fastly .. until i reach 65 mph
!! So impossible to exceed this speed, the engine speed decreases
every time..( except in a small downhill where the "max. speed"
is 70 mph).
I suspect two things: a vacuum advance problem (or a mechanical
advance problem) or a vacuum problem on secondary barrels of the
carb. But i "feel" the opening of the secondary when i smashed
the pedal below 65 mph !!
Advance was set to 12� btdc some weeks ago (no test at high speed
since), because before the setting was too high (20� !!) but car
ran fine with this high advance (and exceed 65 mph ..).
Any advises ?

--
Philippe COURANT (Pau, France)
Imperial 57 Crown convertible
Buick 58 Roadmaster sedan

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