In a large bowl combine soy sauce, garlic, onion, juice of 2 lemons, 7-UP, ground black pepper, dark brown sugar and ketchup. Using a whisk mix and dissolve ingredients really well and pour marinade mixture onto the pork. Cover and set in the fridge at overnight or at least a 4 hours before grilling. Grill on direct heat until pork is done (
I recommend using the Thermapen to check internal temps as a full-proof method for measuring temperature), flipping as necessary to obtain char marks on both sides.