My guess, from what I understand you describe, is that your engine is running too lean. It needs the throttle open far enough to suck enough
fuel. If I am right, you may find the plugs are pale after a run to get the engine warm at 1500 rpm, no choke. That suggests that when you cleaned the carb, you changed some setting. What, would depend on the type of carb. It could be a main needle valve, or the tick-over bypass valve. It could be the float height (my first bet - check the yoke orientation). But like jarod suggests, check the plug colours.
If it were electrical, it may be affecting only one or two cylinders, then the plugs would different colours from each other, but your would hear that at low revs. If the CB points are very badly set, it could have too much advance or retard.
You need to provide more infromation.