While I agree with all that has been said (rebuild the carbs, and while you are at it have Steve install some overflow tubes r.e. hydrolock as a suggestion), a couple of quick things you can try.
1) Drain the float bowls. You should be able to access the carb bowl drain screws from both sides of the bike. Get a length of surgical/aquarium tubing, attach to the nipple at the bottom of the carb bowl, and open the carb drain up. I'd drain all four, then set the petcock to prime (to refill the bowls) and start the bike. The last time I did this, I drained each bowl a second time with the petcock set to prime, so that the fuel could flush over the needle and seat, this seemed to help, and my rough running issues and fuel smell went away. Remember to turn the petcock off (not in the prime position) after you flush each bowl, to avoid a potential hydrolock situation (if one of the needles doesn't seat correctly/still has debris in it).
If you drain into a large cup or bucket, you should see the debris as it drains out, so you can make an assessment as to whether you did any good or not. Once you are done, a quick spin around the block should tell you if this helped.
Again, this doesn't always work, but if you have some grit stuck in the needle and seat, this might help.
2) You can try Seafoam and see if this helps. About half a can per full tank of gas is what I've used. Add to your tank when filling up, and then drive around for an hour or so and see if this helps. Also, if you let the bike sit overnight after your little drive, this will let the Seafoam work on some of the deposits, again take her for a spin in the morning/next day and see if things have improved.
The above two might help a lot, or not much at all. But if you aren't looking forward to yanking the carbs yourself, it cant hurt to try these first. Judging by your MPG figures, however, I'm thinking you'll feel better with a carb rebuild.
On to your second issue, the 'inaccurate' fuel guage. Most (if not all) Connies ship with this problem. In my case, I use about 4 gallons between a full tank and the Red 'E' mark, and once the guage hits the left side of the red wedge on E, I've gone through about 5 gallons. This varies from bike to bike.
Anyways, there are a couple of fixes. Some bend the gas guage float arm to get it to read a little more accurately, others insert a resistor into the fuel guage wiring (where you unplug it from the tank to remove the tank), which often seems to fix it pretty well, with the right resistor of course. Do a forum search on this issue for the particulars.
