I have an 1987 8 hp Evinrude outboard that won't get up to full speed unless the primer is pulled out. It starts great, idles well, and runs but with the primer pushed in it only seems to run at half throttle and slightly surges. I took the line off the carburetor bowl sprayed the carb down with carb cleaner, then ran some sea foam through the bowl. Could this be the fuel pump? Any help would be appreciated