link: check your air mix screws, sounds like they are way out of adjustment...like maybe the washers and o-ring might be reversed. Also, crud in the enrichener (choke) circuit can cause it not to seal properly and cause a mystery rich condition.
baboon: you might take a good look at the o-rings sealing the float bowls and the diaphragms on the slides as a slight leak at either will do exactly what you describe.
