Motor shakes and has little power under load

Symptoms sound most like running very lean. Probably starved for fuel. Check for fuel flow by disconnecting the carb inlet and running the tube into a gallon jug. You should see glugs coming out as you crank. BTW, don't smoke. But, it may pump when cranking and stall at higher speeds. Check that the fuel hoses on the suction side are not soft and collapsing (fuel pump inlet, gas tank outlet). If you never changed to modern "fuel injection" hose, today's ethanol may have gotten them. They can even degrade internally and look OK outside.

If all OK, check that the fuel filter and carb inlet isn't plugged (maybe 1st thing), that the inlet needle moves fine. If a Holley 1920, the internal idle metering block can plug, but some here know how to blow it out from below.

Of course, also check for spark and that the distributor didn't somehow become very advanced.