Habría molado más si hubiera tenido gomas.

Habría molado más si hubiera tenido gomas.
 

Habría molado más si hubiera tenido gomas.

I think this must be a saying unless I am translating this incorrectly. It's from El Heroe Perdido

There's no saying here, given the context of the story, and you didn't provide a translation. ;)

The sentence isn't an exact copy from the story. As I have it, it's "Habría molado más si hubiera tenido algunas gomas para ponerle."
The two friends are talking about a helicopter that was made out of pipe cleaners. The thing actually flew better than expected, after it was launched, but finally plummeted.

"It would have been cooler if I had some rubber bands."

I'm glad that you posted your quote because actually I copied from my book verbatim; so there must be multiple publication version (I recently downloaded mine for the Sony Reader). Anyway, thank you for the descriptive translation with context. I was simply translating it wrong.

You're welcome. Besides having different publications, a book can be translated by different people.

I would have used volado. Molado looks like a typographical error.

Hmm, that is interesting/weird. Why would the author want the book translated by different people in the same language?

....and why would a proofreader allowed such an obvious error.

There is no error, poli. 'Molado' is a perfectly good word. It's the past participle of 'molar' (to be cool, to be neat).