What makes an engine “buck?”

[furyfever]

Going down the road steady-state…45…55 mph can feel engine is not smooth…it “bucks,” it’s a 62 318 poly…my 350 in my 58 DeSoto did this and I put in new condenser…fixed it. Tried it on this 318…didn’t work. Have also changed points and coil too. Still does it. Engine is not a smooth idler either. Did compression test. Range from 125-140 all 8 cylinders. Think it could need a valve adjustment? Thanks…

 

[65sporty]

What are the plugs and wire like? If it's more like a sharp jerk, it's probably an ignition miss caused by a spark plug or wire

 

[furious70]

Lean can cause a surge, usually less severe than a buck.

 

[CBODY67]

Compression numbers look good. "Bucks" are related to tuning. First check for vac leaks, including the vac advance diaphram. Might be plug wires, with one or two that are "leaking" voltage? New ign condensers can be bad, too. Find an old one.

 

[Big_John]

Sounds like a lean surge. What shape is the carb in?

 

[furyfever]

carb is relatively new but I don’t like the way the air/fuel mixture screw adjust. Both don’t do a whole lot.