Why does my engine shake when idling?

[MaximRecoil]

Here's a video of it idling (I had to zoom in for my old camera to pick up the motion):

https://youtu.be/OK4f_yRChAg

It's a 318; I'm not sure what year; probably '72 or '73. I got it running in 2011 after it had sat dormant for at least 17 years, and it has always rocked back and forth slightly like that when idling. It originally had the stock points-type ignition and in 2013 I converted it to electronic ignition using a stock Chrysler electronic ignition distributor, a GM HEI ignition module, and a Ford E-core type ignition coil. It idled smoother after that, but it didn't eliminate the shake altogether. Recently I installed a new coil, distributor cap and rotor, spark plugs, spark plug wires, and HEI module (AC Delco D1906 this time; previously I was using a Standard / Blue Streak LX301) and that didn't make a difference. I even tried a new distributor, and that didn't make a difference either (I've since put the old distributor back in). I've tried various degrees of ignition timing (currently the timing is at about 5 degrees BTDC), none of which made a difference with regard to engine shaking.

Also, the carburetor is a new (at the time) reman BBD 2-bbl that I installed in 2012 or so, which didn't make a difference either. At the same time I removed the intake manifold and cleaned it, which also didn't make a difference. The fuel filter is new as of a few weeks ago.

In 2013 I removed the EGR valve (which was never hooked up in the first place) and put a quarter-inch thick block-off plate and gasket over the port, which didn't make any difference.

As far as I can tell there is no vacuum leak. I've tested every vacuum port on the intake manifold and carburetor by removing the hoses (which makes the engine idle faster) and then plugging the ports, and that makes it idle the way it always does (shake and all). Spraying carburetor cleaner around the base of the intake manifold and carburetor doesn't affect the idle at all.

[green69rt]

That doesn't seem that bad, at all.  Have you checked the motor mounts?  If they are original you may need some new ones...

[MaximRecoil]

Yeah, it isn't bad, but a stock engine shouldn't shake at all when idling, or at least, I've seen plenty that don't shake, including old carbureted 318s like mine.

I've been wondering about the motor mounts. They are definitely old; probably original to the car (or to the engine, which is a few years newer than the car). They aren't broken and the rubber is all there in one piece on each one. How would they cause (or allow) an engine to shake while idling? Does the old rubber get too stiff to absorb the shaking or something?

[70 sublime]

Is the motor and transmission all original and never out of the car ?

I used to have a small block that shook also and never did figure it out
Later after the car was gone I got to wondering if I had grabbed some wrong parts when I put it together as in I needed a torque converter with the balance weight or with no balance weight

[XH29N0G]

I do not know if it was just me, but it looked like there might be a rhythm to the shake.  I couldn't detect a miss, but wonder if something like that, possibly in combination with a mount going, could do something.  Does it lift when revved?

[MaximRecoil]

Is the motor and transmission all original and never out of the car ?

No. The engine is probably a '72 or '73, and I think the 904 transmission is the same or similar year as the engine, due to it having a '70s style damper on it. The car is a '69. The later engine and transmission were already in it when I got the car 26 years ago.

I used to have a small block that shook also and never did figure it out
Later after the car was gone I got to wondering if I had grabbed some wrong parts when I put it together as in I needed a torque converter with the balance weight or with no balance weight

A 318 uses a torque converter without balance weights, because the engine is internally balanced. 360s use balance weights on the torque converter. I assume my torque converter is the right type, because if it wasn't, I would expect a lot of vibration from the engine when driving down the road. My engine feels fairly smooth when driving, even at highway speed.

I do not know if it was just me, but it looked like there might be a rhythm to the shake.  I couldn't detect a miss, but wonder if something like that, possibly in combination with a mount going, could do something.  Does it lift when revved?

Do you mean, does the engine rock to one side when revved? If so, it does a little bit; nothing drastic.

[Challenger340]

Uneven Compression or Ignition Timing is too far advanced.

remove all 8 spark plugs
wire throttle plates wide open
disable the ignition
do a Compression Test on each cylinder....only "4" bumps of the needle per hole.... record the first bump and 4th (final) bump and report back ? but I suspect from your video more than 25 psi variance lowest to highest.