Why does my generac 6250 does not generate any electricity ?

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Generac Air Cooled Generators - Ziller Electric Inc ' Interactive Generac Generator Forum

Could be the fuel tank is not venting properly. When it fails, remove fuel cap and try starting. If it runs replace fuel cap wuth new.

The charger might be bad and you should get a new charger

If you have a Generac Generator which fails to start during a power outage and gives an Error Code 1518 - RPM Sense Loss you can try and manually get the generator restarted very simply. ... The generator should wait 5 seconds and then try and auto-start up to 3 times.
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Shut it off, restart. May have condensation. This happened to me with a generac. OH! OH! OH! Check your fuses! Generator will start, but produce nothing MAY just be a fuse.

Is this the Powermate 6450; Generac 6250; or Coleman 6250 and what engine does it use?

Check the online support of these generators, or look at this operating video for information:

Generac 5000 watt 6250 surge watt generator running

Randy, connect up your volt meter and try manually reving up the engine. Even a few hundred RPM can make a big difference in the generator output.

If that resolves the problem, then you need to adjust the high speed settings on the motor.

Your RPM's are too high. There is no voltage regulator in coleman generators (generator is actually made by generac) and is 100% dependent on engine speed. There is a screw under the tank when your looking in from the recoil side. It controls the governor arm. Screw it in and it incresses the rpm, out decrease. Plug something in that draws a decent load while setting the rpms since you want it to put out 120 and 240 underload. Your idle voltage does not matter.