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 - American Car Club de France (ACCF) : http://www.accf.com - Chrysler Imperial France : http://www.ifrance.com/c-i-f - Cadillac " Standard of Excellence " : http://www.ifrance.com/accf-cad - SportsCars : http://www.ifrance.com/accf-sprtcar