My 1404 Imp seems to lack power under moderate load. The vacuum advance seems to work ok, Points ok, But the plugs look kinda whiter than normal. Maybe the carb is too lean. The engine does not miss. Ive never adjusted the Carb after a friend rebuilt it for me a few years ago. Anyone know what screws to adjust to make the fuel/air mixture more rich? Any troubleshooting suggestions? I replaced all ignition parts and tuned up about a 100 hrs ago.