need help with adding fuel pump to non fuel pump mtor

I have a Husqvarna lgt2654 that had an intek vtwin 26hp engine that has a fuel pump. The plastic drain plug malfunctioned and the oil leaked out and threw a rod through the block. I had a 20hp intek single cylinder that came off a craftsman that was gravity fed. I installed the new engine and drlled a hole in the valve cover to power the fuel pump and its not running very good. The carb seems to be running lean. my main question is does anyone know if the carb that was gravity fed is capable of running with a fuel pump. The engine is Model #31P977-0670-E1. The carb is a nikki 792036. It has a new plug, new air filter, carb has been taken apart and cleaned twice and seafoam treatment in the gas. Im going to check the valve clearance as soon as I find the specs on them.