I got my car (66 cupe) about a month ago, and it ran like a dreem till about two weeks ago, it gradully got worse but ill explain whats happening to the best of my ability.

At about 20mph it starts shaking and gets the worst at 30mph and goes away by 40mph from 40-50mph It drives smooth so long I keep the peddle down far enough to sustain the speed or have the peddle completely backed off. at about 50mph it dose the same as at 20mph but doesn't get better.

Ive checked the U-Joints, Balance, and motor mounts so far and they are fine so dose anyone know what else it could be?

I kinda have a stupid idea but here goes.
My carburetor has been doing a bad job at idle, it will run smooth for like 3 seconds then the car will run rough as if the idle mixture was off then goes back after like one second (and repeats this continully) Ive reset the idle mixture screws to 1 1/2 - 2 turns several times and didn't fix it so what I thought was possibly since I cant fix that problem (the problem feels the same as when I'm driving just not nearly as bad) I thought that maybe when I'm driving the engine is getting a bad air fuel mixture and shaking the car when the peddle was give the bad mixture, because the peddle shakes the same as the car but I could just be exsadurating because the stearing wheel and shifter do the same as the peddle.

Anyway, any ideas how to fix it or comments on my stupid idea would be great.

 

well not that anyone helped but I was wrong, it was my U-joints.

 

this might get answered faster in the general tech area

 

wow you waited a whole 4 hours for an answer...shame on us for not stopping what we were doing to help you your more important than anyone else..

 

Well first, sry I didnt know I was in the wrong area, and seccond I posted that before I went to bed and woke up and took it to the auto shop and replyed once It was figured out.