I didn't spend too much time trying to make my keihin run right. I know my problem was not air leaks. But the 'cough' was annoying. It wasn't as bad as some I've seen. I have the same problem on my '04 FLHT and I'm not going to spend much time screwing with it, either. Sure, one can diddle with the carb till he gets it 'right', but if the damn regulators would leave the OEM's alone, maybe we wouldn't have to fix these things.
As to gas mileage, only lately does that have a factor. Before, I didn't even watch that other than to check for changes in engine preformance.

Just my opinion.

 

They all are lean from the factory it's a cheap way to meet gov. emissions mandates for manufacturers . We've had to tweak HD carbs right off the showroom floor since the late 70's and the beginning of the green movement . Don't bitch in Ca. it's several orders of magnitude worse .