Small Engines (Lawn Mowers, etc.): 6HP Robin engine surging help please???, robin subaru, adjustment screw

Question
Hi from Western Australia!!

I have a Robin Subaru 6HP engine that is giving me some dramas. It is an EH172D (model). The trouble i am having is unless the choke is on half way, the engine continually surges up and down in revs. Maybe the governor or carb? I did clean up the carb and there was solid material in there. The main jet screws out and is clean but how di i get the main jet "nozzel" out? it seems to be very tight, dont want to break it???

Cheers for any help
Mat

Answer
Usually a four cycle engine will only surge if there is an air leak Orlean fuel condition.  The easiest to check for is the early check or the carburetor mounts including the intake manifold and moaning gaskets.  Check the fuel line be sure there is no leaks where air could be drawn into the fuel flow check the carburetor or the fuel enters to be sure fitting is tight next would be lead running conditions meaning that the engine operates as if it's running out of gas the best way to repair this is to clean the fuel system.  Start with the fuel cap be sure the vent is operating properly.  Next flush the fuel tank being sure to back flush where the fuel comes out.  Next replace your fuel filter and fuel lines.  Next remove the carburetor and completely disassemble clean every air and fuel passages with a wire from a wire tie and blowout with carburetor cleaner or compressed air purchase a carburetor kit from your dealer and install it per instructions.  Set the mounting screws at two turns off of seat and start the engine let it warm up a little bit and then make the adjustments to the carburetor.  Do not run the engine to lead turned the adjustment screw out until the engine floods then turn it in to where it starbursts for fuel then back it off about halfway in between.  I think this should help you out