nearly all the modern gensets have a plunger type affair in bottom or side of carb thats electricaly controlled. usualy a single wire to it.its purpose is to cut off fuel flow in case of accident,emergencies,fire etc.basicaly to stop engine from pumping fuel into a fire or something of that nature.they normally dont shut off fuel to the engine persay,but block the main jet passages in carb. this gives a much faster shutdown since carb doesnt have to run out of fuel in bowl.in your onan carb ,if i recall on your model correctly its in the bottm of carb, has a single white wire to it.THAT for all intent and purposes is the main jet in your carb and if its closed,engine runs out of fuel in just a second.if your carb is blocked up very often ,( more often than not) unscrewing this will allow you to pullit out,and carb bowl will drop off.once its in your hand main jet passages will be in the tube attached to the end of solenoid ,and thats basically all the jets/orifices in the carb.clean bowl of course,and clean the orifices on solenoid good. before reinstalling spray some carb cleaner up into body of carb where tube goes in,because its common for bits of orings to get lodged there.make sure orings are good on solenoid and reinstall. to check power,use a voltmeter and check voltage at white wire and body of genset,should have voltage with switch held in start position(engine cranking).if voltage goes away as soon as engine starts,you most likely have either a exiter voltage problem,or a control board. if voltage stays and engine dies, either you have a problem with the plunger type solenoid itself,or a fuel delivery problem. (note) they WONT seem to pump much fuel when engine is cranking,simply because they are cranking at maybe 100-200 rpms,once engine starts its running several times that and it will pump far more. if you question fuel delivery system up to the carb simply gravity feed your fuel directly into carb from a safe source and bypass it all. if engine runs you know you have a fuel or fuel delivery problem. first thing i would do is try some fresh fuel if it were mine. if i recall right exciter voltage fault code is 33 (going by a old mans memory here so dont trust that too far),so that means at least the control board says you have it.once its past that point fault codes wont show a problem so also check for a broken or loose/corroded connection between there and carb. any fault basicaly thats not found electrically most likely defaults to 36 or a fuel problem. if engine wont run with no electrical faults thats the next most logical step,but fault codes wont show up if the electrical problem is past the point where voltage is tested if that makes any sense. hope this helps. I dont think ive ever seen a genset on the roof,must be a new thing they are doing.lokks to me as if that would amplify the noise a genset makes sort of like being inside a drum.