I drive a 63 Valiant with a 225 slant. Has approx 17,000 miles since the rebuild. New carb about 3 months ago, just tuned; plugs wires cap and valve lash adjustment. Runs great however sitting at an idle it kinda chugs. Only word I can think of to describe it. Any suggestions?

Tune-up parts and technique suggestions in this thread; review them to make sure they were followed reasonably closely (especially with regard to spark plugs and plug gaskets). Rough idle can be caused by valves set too tight, for example if they are set cold rather than hot; see the valve adjustment procedure. Tell us more about the carburetor; is it really new, or is it a "remanufactured" item?

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Too many people who were born on third base actually believe they've hit a triple.

"Chugging" with black smoke out the tailpipe, during cold start-up usually points to a mis-adjusted choke.

To test, remove the air cleaner prior to starting the car cold.
"Set" the choke as usual. (pump the gas once)
Inspect the carb to see if the choke flap has closed.

Start the car, it should start and fast idle. Return to the carb. and see if the choke flap is open about 1/4 to 1/3 the way.

At this point, the "chugging" should be happening so reach-in and slowly pull the choke flap open more.

If the chugging stops and the idle improves, adjust the choke flap pull-off to open the choke more, right after start-up.
DD

Thanks for the info. I believe the carburetor to be new. It's a Holley one barrel I bought from a guy who had a bunch of old new stock. Came in the original box with instructions and linkage grommet. The carburetor and choke seem to be operating fine. I think I have the valves adjusted correctly. I adjust them at operating temperature while running. However I did not know about the spark plug washers, it makes sense.