I have a Honda EX1000 which starts well, but the output voltage drops if any load is applied.

This is not critical in most cases, but as I wish to charge my RV batteries with a big charger, I want to have at least 50% of the 1000 watts ( being 40 amp x 12 Volt max) but even at 25% load, the voltage drops below 100 v so my charger does not work.

There is a screw that adjusts the speed I think, and if I screw manually to get the 110 v with some load, then I can get 15 amp plus charging, all is well, BUT when I disconnect the load (charger)the voltage climbs up very fast, past 130 volts. Not ideal, as I need to keep a constant eye on what voltage is output, depending on the load, and adjust the screw accordingly.

I suspect the governor is not working well.

Would anyone know where to get a repairs manual ?

Do you think it is a question or maintenance and adjustment, OR would I have to replace the governor (or is the problem elsewhere)?