I'm just kinda winging it here with your info.
Being a 5hp I would guess that it's probably around 1800-2000 watts.
Does it have only 120v recepts, NO 240 recept?
Sounds like it doing well. I would let it run with a light load of 600-1000 watts for awhile.
Being a 5hp it would mainly be used for emergency lighting and they make a real good camping gen and will operate a regular size refrig or freezer in a emergency, one at a time, and a camper window type A/C up to about 5-8000BTU's
Sometimes they will have kw rating labeled somewhere around the recepts, or some type of max warnings.
To get more precise
instead of using engine rpm's and a tachometer, a Hertz meter (HZ) or frequency meter that will read 55-65 Hz.
Normal utility power is 60 cps (cycles per second) or 60 Hz (Hertz) Hertz and cps is same thing.
With a hertz meter you would set the
no load Hz at about 62-63 and at
80% of rated KW (kilowatt load) One KW is 1000 watts)so if the gen is a 1800w unit (1.8KW)is 1440 watts or about 12 amp, 120 volt resistance load. (a electric heater) it may dip and stay at around 58Hz, so you are
averaging around 60Hz loaded and no load. The large spring associated with the governor lever is to set the gov sensitivity for minimum hunting from load to no load. If it don't have auto idle you can set the idle adjust screw in to prevent a low dip when it loads up initially until the governor picks up the load and reduce the hunting dip in Hz somewhat.
Those small gen''s will really struggle when trying to do a motor load, because when a electric motor or electric compressor first starts it draws about 6 times it's name[plate current when it first starts, therefore when checking the samll emergency gen on a appliance like a fridge or window A/C you have to be careful and not overload the gen.
You are blessed that it did not have the obselete Tecumseh engine.
Do not be surprised if you check and find some of the Briggs parts such as the SPECIAL crankshaft is NLA.
Did you have to excite the unit and does it have any circuit breakers or fuses on the gen?
Post up a picture of the rig?
Some of the $20 wal mart electrical testers will read in the 60 Hz range. Some use a Kill-O-watt meter at about $20.
You read the owners manual on-line and see them on flea bay. If you use a KIll-o-watt meter use a extension cord for the tester so as it don't have to ride on the vibrating genny chassis.