Other things you can try is to thicken the outer airfoil by about an extra 2 or 3% compared to the root. The thicker airfoil is more resistant to stalling thanks to the extra thickness and probably the extra camber if you're using a flat bottomed airfoil. If you use something like Profili to thicken it try increasing the camber by an extra .5 to 1% and move the max camber position forward to about the 40% point. This is all very crude in this day of high zoot airfoil design using pressure distributions and all but these rules of thumb were suggested in many model magazines back in the early days. All else being equal thicker sections and sections with more camber stall later. Of course the extra camber will make inverted stalls occur easier so you may want to just stay with a thicker airfoil. But watch how you thicken it so the camber stays constant. Moving the max thickness of the airfoil forward a bit may also help resist the stall.