answer to original post problem is starting if the engine doesnt have a centrifugal clutch coz compressors are bad news to start direct drive especially if there is any pressure already up.
Still hard to do from cold believe me coz you have two flywheels all the pistons cold sticky oil and you have to put all that energy through a piece of string and your arm, take it from someone who has a permanent broken wrist bones from it, any restriction slows the engine flywheel and prevents the engine from gaining speed and they easily stall out whereas getting an engine with a centrifugal clutch all you are doing is starting the engine as soon as the speed picks up the compressor then starts to spinCould put a T piece with a check and a ball valve on the line between the compressor and tank. Open the valve, crank the engine which will be easy as the pumped air is free to leave then close the valve to send it to the tank.
Still hard to do from cold believe me coz you have two flywheels all the pistons cold sticky oil and you have to put all that energy through a piece of string and your arm, take it from someone who has a permanent broken wrist bones from it, any restriction slows the engine flywheel and prevents the engine from gaining speed and they easily stall out whereas getting an engine with a centrifugal clutch all you are doing is starting the engine as soon as the speed picks up the compressor then starts to spin
