It's a LM as you said it has the idle adjuster screw.G4's didn't have that.I'll get some pictures for you of the poppet value and show you what I mean.
In the mean time if you have something like start ya bastard,start the engine and squirt some down the air filter tube and see if it revs or not.
That will help as to whether or not the carby is working correctly it may be something else.
