Part 35 sometimes gets stuck inside the carb and could be damaged. If you haven’t already done so, inspect part 35 that little piece of plastic can get damaged or broken especially when soaking in carb cleaner etc.
other than that, try hooking it up to a timing light when running and make sure your not dropping a cylinder. I had a condenser wire that was damaged by the flywheel spinning and would intermittently short out . Drove me crazy until I noticed the small nick of exposed wire. Also I would stick with OMC fuel pumps. They are expensive but I’ve had issues using cheap aftermarket fuel pumps.
