When you say good spark from both wires, do you mean spark will jump 1/4" consistent blue spark in open air(spark tester)? Holding plug to block only shows .030 air gap spark, and may not be enough spark to fire under compression. And if you didn't change the plug wires, you may have a faulty connection in one of the carb boots (you can pull boot, cut 1/4" off the wire and reconnect).
Other possibles: Did you re-install the carb linkage after carb kit (been there). Otherwise, try a cylinder drop test.. run motor at high idle and pull one plug wire at a time w/insulated pliers. If it immediately dies when pulling one of the wires, then the other wire's cylinder isn't firing correctly.. due to spark, plug, bad leaf (reed) valve, compression..
Post back if you're still having issues after above test to rule out ignition/compression problems. Also, if motor passes above drop test, try pulling the choke briefly to see if it'll pick up rpm's at higher throttle setting (would normally flood and die very quickly). You can also pull the fuel line at the carb and open vent and fuel petcock and check flow to carb.. should have a good steady stream of fuel.
Good luck!
