It started a few weeks ago. My boat would run great at high rpms, but not so great at low rpms. It runs at low rpms but it sounds like its picking up a cylinder. I have good spark and good compression (135 on all). The rpms jump a few hundred rpms. It also has been fouling the plugs more often. I was thinking the fuel pump may be going out, and the vacuum leak is causing the jump in rpm. I sprayed cleaner in the carbs and put a new set of plugs in it and no difference. Any advice?