In Australia, the recommended Yamalube for generators is SAE 10W-30, not the 10W-40 as per the owners guide.
This stuff here: https://shop.yamaha-motor.com.au/accessories/yamalube/yamalube/golf-and-power-products/engine-oils/lub-10w30-gg-12
There is even a picture of an EF2400iS generator on...