With a brand new carb, weak ignition seems the most likely problem. However, I'd expect other indications to accompany this...hard starting, especially when cold, and some misfiring, possibly showing up as an uneven idle, or lack of power at high rpm. IMO, first step is getting the ignition performing up-to-snuff. These old-school breaker point ignitions work quite well, with visible & audible spark production that would do justice to a CDI...when everything is in tip-top condition.
Source a new spark plug, then bench test the ignition. If you don't see/hear a nice, miniature, lightning storm at the plug electrodes, time to find out why and make the appropriate correction. That does not leave many places to look, i.e. points & condenser. It doesn't take much to foul point contacts and they don't take kindly to filing. Condenser failures have also become much more commonplace than they ever were, though I suspect that some are caused by overheating, during soldering. Could be that a new plug gets you back up & running again.
Most of the reproduction carbs I've installed & tuned have been on the rich side, as-delivered. It usually takes a 1-2 groove height adjustment, of the jet needle, and a slight bit of tweaking of the throttle stop & pilot airbleed screws. Easy to figure out when you've gone too lean, you'll get bogging if it's the main fuel circuit, weak idle/hard starting/stalling if it's the pilot circuit. Other things that can foul a plug are excessive low-speed operation, bad fuel (which can mean a switch from summer to winter blend) and ambient air temp. The air/fuel mixture becomes effectively leaner as ambient air temp decreases; however, fuel atomization also degrades and it's possible to get pooling if enough gasoline condenses out of suspension, from the incoming air/fuel stream.
If the engine has an oil control problem, substantial enough to foul plugs, then you should see some bluish-white exhaust smoke...accompanied by that lovely, acrid, smell of burning motor oil
. Other traces...oiled plug threads, oil in the exhaust (port, or muffler), blackened & shiny intake port, oily valve stems.
Source a new spark plug, then bench test the ignition. If you don't see/hear a nice, miniature, lightning storm at the plug electrodes, time to find out why and make the appropriate correction. That does not leave many places to look, i.e. points & condenser. It doesn't take much to foul point contacts and they don't take kindly to filing. Condenser failures have also become much more commonplace than they ever were, though I suspect that some are caused by overheating, during soldering. Could be that a new plug gets you back up & running again.
Most of the reproduction carbs I've installed & tuned have been on the rich side, as-delivered. It usually takes a 1-2 groove height adjustment, of the jet needle, and a slight bit of tweaking of the throttle stop & pilot airbleed screws. Easy to figure out when you've gone too lean, you'll get bogging if it's the main fuel circuit, weak idle/hard starting/stalling if it's the pilot circuit. Other things that can foul a plug are excessive low-speed operation, bad fuel (which can mean a switch from summer to winter blend) and ambient air temp. The air/fuel mixture becomes effectively leaner as ambient air temp decreases; however, fuel atomization also degrades and it's possible to get pooling if enough gasoline condenses out of suspension, from the incoming air/fuel stream.
If the engine has an oil control problem, substantial enough to foul plugs, then you should see some bluish-white exhaust smoke...accompanied by that lovely, acrid, smell of burning motor oil
. Other traces...oiled plug threads, oil in the exhaust (port, or muffler), blackened & shiny intake port, oily valve stems.
