Start by checking the float setting and making sure there's nothing blocking the needle / seat assembly. I'd pull the top off the carb and check for crud in the bottom of the float bowl. Might be a good idea to plumb a filter into the line ahead of the carb. Stupid as this sounds, next look for vacuum leaks, and check your timing . Set the idle by leaning the mixture screws until it begins to lose RPM, that's usually done by turning the screws in. I'd also check to make sure the things fully warmed up when you set it. It will want to be richer when it's cold than it will hot.