Jeez - do you coast downhill with the engine switched off? Joke!
Seriously, I'd be very pleased to get 42mpg out of the 'bird. It could be the riding I do, currently short distances on mainly B roads. If I was sat on a M-way/A road in top gear no doubt it would be better. Having said that, the owners groups reckon its a thirsty beast. Interestingly, the FI ones are less economical, & a bit down on power, compared to the earlier carbed ones.
My previous ZX-9R would often get 50mpg on long runs, when I travelled for work.