Picked up a used Mantis (SV-4/A engine) that will just not idle. I've cleaned and rebuild the carburetor, fresh gas/oil mix, played with the idle mix screw, etc. Runs well at full and medium throttle but simply will not idle even with idle adjust screw all the way in. Also checked the muffler screen which is clean. So, looking for any additional suggestions! Does anyone know if the later carburetors with primer could be used with this engine? I know I'd have to change the tank plug and fuel lines but that's easy.

Thanks in advance for any suggestions!