In a large skillet, heat vegetable oil until hot. Stir fry pork until it is no longer pink. Add the garlic, carrots, celery, bean sprouts and scallions. Season with soy sauce, black pepper and salt. Stir fry until all ingredients are cooked, but still crunchy (about 3 minutes). Remove from heat. Set aside to cool.
Peel lumpia wrappers.
Take one lumpia wrapper and place it in front of you in the shape of a diamond.
Spoon 2 to 3 tablespoons of the cooled lumpia mixture on the the closest edge closest to you, leaving a 1 1/2 inch space at both ends.
Grab the bottom edge of the wrapper and roll it up and over the filling until over two-thirds of the way complete. Tuck in the ends of both sides and roll until one inch of the wrapper remains.
Moisten the top edge of the exposed end with the egg yolk mixture and roll the egg roll over it to seal. Place the lumpia on its seam on a large platter. Continue rolling with the rest of the filling and lumpia wrappers.
To cook the lumpia, heat a large frying pan with vegetable oil to 1/2 inch depth over medium high heat. minutes. Gently slide a few lumpia into the oil. The lumpia take about 3-5 minutes to cook on all sides. Make sure all sides are golden brown. Drain on paper towels. Serve immediately.