Toss pork and salt together in large bowl and let sit for 20 min. Meanwhile whisk ketchup, sugar, chili powder, cornstarch, liquid smoke, and cayenne together in bowl. Set aside 1 1/2 Tbsp ketchup mixture.
Add remaining ketchup mixture to pork and toss to coat. Thread pork onto 4 - 12” metal skewers, leaving 1/4“ between pieces. Spray both sides of meat generously with oil spray.
Cook on hot grill until well charred, 3-4 min. Flip skewers, brush with reserved ketchup mixture, and continue to grill until second side is well charred and meat registers 140 deg., 3-4 minutes longer.
Transfer to serving platter, tent loosely with foil, and let rest for 5 min.
Alternative: Cook pieces in hot skillet turning to brown all sides and until 140 deg. Add remaining sauce near end.