i meant 6500w not kw

do you mean the diesel motor is not running rite, bogging down or the generator part, that makes the electricity, is bogging down, not putting out enuf voltage??? how long did it sit up without being run? does it stay out of the moisture?

Check your fuel filter, sounds like you could well have water in your fuel. Sometimes you can bleed the filter and check for water. Just a thought.

Have you noticed a change in the RPMs or sound of the engin when this happens, if so it could be fuel supply, if not there is a rheostat or voltage regulator on that machine that might be going bad.

the generator itself doesn't really change tone that much, if at all. its just like the voltage drops off then picks back up. someone at the camp said it could be the brushes but like i said it got us all scratching our heads. i can say that the starter has been replaced within the last year.

I had the same issue with my diesel generator and it turned out to be a fuel problem. Changed the fuel filter and everything is fine now.

Hope this helps

The brushes or their only to provide excitation to the rotor, they play no role in generation; voltage generation is controlled by two things RPM speed and a voltage regulator.
You could put a strope light on the shaft to see if RPMs drop off during this dimming of lights,if you are not noticing an audible change in the machine.

I would guess you changed the fuel filters , something to look at is if your Yanmar has banjo type fitting on the fuel lines , and it most probally does then you most probally have a screen filter inside the fitting , if you have a mechanical fuel lift pump it would be on the hose or tube coming into the pump to protect the pump from trash , a banjo fitting is a hex headed bolt with a passage drilled thru it , the bolt goes into a round fitting that has a tube or nipple coming off of it , you take out the bolt without losing the sealing washers on top and bottom of the round fitting , the bolt is threaded inside and a plastic strainer screen screws down into it , a flat screw driver will screw it out , if you have an electric fuel lift pump it would be before the pump

Did you try Shaking the thing or at least a good kick or two ? ? I found cussin' at em' does wonders too.... LOl !

Good luck. Good info above.R