No power since 8am now 3:30pm PoCo thinks they'll have it back on by tomorrow at 3pm.  So it's on to the generator for keeping the business running.  Never mind we're in the middle of a town of 50k and everyone else has power.

It is an obnoxious 5kW Briggs&Stratton thats howling away.  Now the noise is bad enough but it is doing this bop.. bop... bopbop..bopbopbop thing with its exhaust note.  It is extremely annoying.  Does anyone know what causes this?  Each bop is accompanied by a power disturbance.  These things happen about 20-40times a minute.  They completely block every ones ability to "tune out" the generator.  They decrease with load.

Is this an engine problem, or a governor hunting problem, or?

It could be 'missing'.  This may be caused by several problems, but on little gas-powered generators, it's often the result of the generator trying to maintain proper RPM at low loads.  I've actually added load to generators used for test power in the field, finding that the generator will run more smoothly and with better regulation when loaded around 50%.  A resistance space heater or a set of halogen work lights worked well for me in this application.

Those other problems?  Bad fuel.  dirty carburetor.  Old or fouled spark plug.  Etc.

Is your load swinging at all.  The worst problem that I have had with the popping exhaust noise problem with Briggs is when they weren't fully loaded and the load was fluctuating causing the fuel mixture to be constantly changing.  The popopopoppping noise you describe sounds like when the load backs off (and when it would then be fuel rich as Bill W mentions).  If I could ever solidly load them they seemed to line out and run better.

Someone needs to go the break room and put some lunch to heat in the toaster oven.  That will load the dickens out of a small generator.

I, too, think it is running rich and coughing.

1) Try adjusting the high speed fuel needle valve.  



On many 8 & 10HP engines the high speed valve is on the lower left of the graphic, extending out at an angle from the bottom of the bowl of the float carbs.  

CW closing (tightening) the needlevavle will lean the mixture at load.

Tighten it an 1/8 turn at time, wait and see what sort of change in performance you get.  You can always go back to where you started.

2) If the float is sticking because its gummy, then some cleaner might loosen it up.  I've always hoped chemical solutions would work, but have never had them do so.

My generator Briggs isn't as bad as the Tecumseh on my snowblower.   The driveway descends in elevation to the road and I need one high speed carb adjustment blowing snow 'down' the driveway and another adjustment blowing snow 'up' the drive.

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