geoff wrote:
I bought a little 900W genny the other week

It says to use 10/30 oil, I've got some SAE 20 fork oil lying around,
should that be OK ?

When are you most likely to use it? Power outage in the winter and wishing
to run a critical unit? Might be a bugger to start. For the amount of oil
involved, I think I would spend the pennies on some 10/30.

It really depends upon the intended use, I guess.