The blade should be set to take a very shallow cut.
The blade should be well supported from behind. If the backer is worn, and the blade rocks the slightest bit, you'll have chatter and grab.
The throat opening between blade and sole ideally should be a small gap, 1/32 or less for hard maple with curl. I doubt you'll get a spokeshave with an adjustable gap, which is rare on a spokeshave.
Maybe your sharpening angle is too steep?