[grivera]

Pontiac balancers are all neutral balanced, IIRC. The difference with an internally balanced engine would be the flex plate/flywheel would also be neutral balanced vs an own where the flex plate/flywheel have an imbalance.

[Lee]

If you have access to spares, maybe try a different carb and distributor. Those are easier to swap around than flywheels :-)

[Tim Corcoran]

Update:

Removed the trans, clutch, pressure plate and flywheel. Installed two different OEM flex plates and the vibration is still present at 1800 RPM. I did notice that the clutch springs have been making contact with the bolts attaching the flywheel. The flywheel is .135 under the OEM spec of .960. Those issues are unrelated to the vibration but need to be resolved. I am baffled as the what is causing the vibration. It appears the flywheel is an aftermarket SFI unit. (see pic)

[Tim Corcoran]

Originally Posted by Lee

If you have access to spares, maybe try a different carb and distributor. Those are easier to swap around than flywheels :-)

Since the vibration is still present during deceleration with my food off the gas I doubt it is carb or timing.

[Holeshot71]

Maybe try a neutral balanced flywheel/flexplate if you haven’t yet?

[steve25]

Take advantage of doing this experiment if you still have the clutch removed.

Take one of the clutch mounting bolts ( or a long enough different bolt ) and stack two big washers under when you bolt it to the flywheel.

Start the motor and hopefully one of 3 things will then take place .

1) the vibration will be less or gone.

2) there will be no change .

3) the vibration will be worse.
If the vibration is worse the move the bolt washer combo across to the other side of the flywheel as best as possible to be 180 degrees out .

Try this in all six clutch mounting bolts holes or until you hopefully get some kind of result either way.