I just picked up a 1980 SP400 the other day and need a little direction in making it run correctly. It idles great but just off idle it boggs real bad and is tough to get it to build revs above that point. It lasts from 2500 to about 4000 rpm. I was guessing plugged up pilot jet. It took the carb apart and inspected and cleaned everything. I started playing with the pilot jet adjustment, I unscrewed the screw a fair bit. It runs better but it still boggs and smells like it is running rich.