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Did you use a new carb. gasket when you installed the carb.? Have you checked for vacuum leaks? Is it any better when the engine warms up? Does it stumble when you rev. it in park?
Fuel starvation? Do a fuel volume test. Look for kinked fuel lines.
Make sure you're getting fuel as Vile said, but I've had similar issues more than once from a bad spark plug wire or one that isn't making proper connection. With the engine idling pull off a plug wire and note the rpm drop. Put it back on and do another...repeat until you've found one that doesn't change the rpm much. If you do find one, that cylinder isn't doing its job either because of poor fire or possibly an internal engine problem.