Thanks,  I knew it would move but I didn't know if there was enough clearance to run the engine with the converter pushed out of the way.

Aren't there weights on the flexplate? This is now a windsor style system, bellhousing flexplate converter. At least this will show if it is the engine or something else, correct?

Last edited by Scott (9/27/2014 9:43 AM)

Hi Pablo,  Thanks for the reply.  My torque converter has a drain plug that needs to poke through a hole in the flex plate. I don't know how many access holes the flexplate has for this but I will look at it. Idle is set at 600 out of gear according to my truck indash tach that I removed and use to test rpms.

Last edited by Scott (9/27/2014 10:19 AM)

.
if it only vibrates at idle and goes away above idle it is not out of balance. look for a plugged idle circuit or air leak. if one of the idle sctrews has no affect it is plugged.
.

If it WAS out-of-balance.....it would get worse as the speed increased.....not go away. 
I would check that carb again and maybe advance the timing and then slow the idle back down.
The motor mounts ARE in good shape aren't they?!
6sal6

Scott wrote:

At this point I feel kind of stupid.  That makes sense.

what makes sense?

repsitioning/reclocking  the converter will do nothing, 0 nada, zip...
 

Last edited by barnett468 (9/29/2014 2:21 AM)

I had a car years ago do the same type of annoyance only at idle. We tried everything including now carb and all the gaskets. I then remembered another car earlier that was similar. That one had a valve starting to go bad, but was a slight leak and only could be felt at idle. So, I pulled the valve cover and checked the valve adjustments. One valve was cranked down just to the point that the hydraulic lifter was mostly collapsed but just would let the valve almost close. I adjusted the valves all to spec and it fixed the idle issue. One more thing to consider. Of course we assume all the tune up things have been gone over too as a bad plug/ plug wire can do the same.

Unbalance forces increase with the square of engine speed - so as mentioned if your engine is out of balance it will get much worse at higher engine speeds.  Speed sensitivity where the vibration gets much worse and certain engine speeds, wheel speeds, or driveshaft speeds is knows as resonance - where an excitation frequency coincides with some natural frequency of the engine mounts, suspension, etc..  So, you may indeed have a resonance related issue with the engine at idle even if it is fairly well balanced and this resonant condition may be at engine speed or at two times engine speed which in reciprocating machines is referred to as reciprocating unbalance - an up-stroke and down-stroke of the piston for each revolution of the crank.  It can also be at 1/2 times running speed if it is one cylinder that is not firing the same as the others in a four-stroke engine/motor.  Some things that could cause the resonant condition are the motor mounts, the transmission mount, and the exhaust system.  Depending on how the exhaust system is hung, you can have a significant natural frequency of the exhaust system and muffler right at idle speed that will shake the entire car.

It sounds a lot like you have an fuel, air, or valve issue as others have mentioned but it might be a good idea to check under the car when idling in gear to see if something else is causing your problem - what I often refer to as the tail wagging the dog.  You can focus all your attention on the dog (the motor) when the problem can be something else entirely.  For mounts, you can have problems if they are too soft or too hard - before they break elastomeric compounds like the rubber in motor mounts gets harder and harder and the change in stiffness will change the natural frequency of the engine on the mounts and murphy's law of resonance says that it will change the natural frequency to a speed that is most aggravating like idle.

If you are not seeing any fluctuations on the vacuum gauge, you may be above the response time of the needle to see the variations in vacuum.  For fun, have someone put the car in gear and hold the brakes.  Slowly drop idle speed way down to see if the gauge still reads steady as you drop it down just before it stalls.

Last, make sure you don't have any direct contact between the engine or transmission and the body/frame.  At low engine speeds this may transmit a lot of movement into the body that feels like a vibration problem.

Or, you can pretend that the motor has a big cam in it causing it to shake at idle.  Make sure you are running appropriate oil additives so you don't flatten the cam but this would probably not have happened immediately when you started the engine.

My 3rd rebuilt carburetor did the trick. It's very smooth now.

Scott wrote:

My 3rd rebuilt carburetor did the trick. It's very smooth now.

 
Was this actually the third physical carb, or the third rebuild? If the third carb, where did you source them from?