fuel question - sounds like the floater in the tank (to measure level) could be sticking. might wanna pull it up and check.

exhaust question - i would be pretty certain its the bigger piping, esp if there is no resonator.

i just had a 2.25" exhaust custom made for my B18B, and it took the guy 3 mufflers and two resonators to get it quiet without rasp, so if its just a muffler on big pipe, i would bet a resonator/diff. muffler would help.

g/l