I have a 1975 cb550. I got the head gasket replaced which went fine (so i hear), and at the time of the servicing the air filter was replaced which was apparently filthy. Fuel economy is now down from about 35 to 22 mpg. also, after driving for a few blocks at a steady speed, it starts to stutter a bit as when the fuel´s getting low and the bike´s telling you to switch to reserve. it also does this stutter just initially when you give a lot of gas (then it revs up just fine). fuel flow is fine, i changed my in line filters. could the carbs need to be adjusted to a new air filter? thoughts?