Idle drop in Drive causing issues.

[wearymicrobe]

Kind of a strange question. Got one of my 356 motors built up and installed. Car runs great, idles great, manifold pressure is doing exactly what it should.

But at idle and only in gear the car has a miss and its showing on the vacuum gauge on the manifold. Its moving around -~3 inches with no real pattern, drop it into neutral and it will read a solid -22 inches, drops smoothly and the car freaking roars in neutral, definitely dragging though off idle in gear.   

So couple questions. I am assuming that it is load on the motor and the carb causing about a 200rpm drop in RPM in drive. I have the motor set at ~1400rpm cold, 800 rpm in neutral and about 600 in drive. I swear it sounds just like a sticking/maladjusted  valve but as soon as I bring the RPM up it goes away.  At 600 the car will creep forward.

My normal SOP would be to retard the timing about 3-4 degrees and that cleans it up a small amount but I know I am not hitting the book curve above 2000rpm then.

Also do OEM 57 Cadillac's have fuel pressure regulators or are they built into the factory fuel pump. I have new pressure gauge coming in this week and I am checking the floats tonight just to be safe. Is there a check valve in the hydromatic brakes that I might not know about and am missing say a check valve.

If I had another wide-bore AFB that I trusted I would swap it out but I don't right now.

[wearymicrobe]

Penalic spacer failure and a bad hot idle valve means its not going to run. Got a new carb on the way as I am sick of dealing with the old carter rebuild parts cost. Went to a 1406 will bolt right up except for the kick-down which I will have to fab.