I have a 2007 Honda Shadow Aero 750. I bought it in 2014. (My first motorcycle) I have intentionally run it till I had to switch to reserve to check how many miles I can go on a full tank. The first time I went 120 miles on it before having to flip to reserve. The second time was only 116 miles. Is this typical mileage? Or should I have a mechanic check it out? I now start watching for a gas station at 100 miles. I'm getting ready to go on a long trip and really hate that I have to make everybody stop so frequently in order for me to fuel up. Any thoughts or suggestions?
According to this website, the average MPG for a 2007 Honda Shadow 750 is ~50MPG (based on 14 bikes, 509 fuel ups, and over 61k miles of driving). Your tank, excluding a reserve of 0.9 gallons, is 2.8 gallons. Simple math is telling me if your bike was "average", you should be able to go 140 miles before you hit the reserve. To me, if you're only hitting ~110-114 miles, I'd take it to the shop and see if they could help your bike out for you. You are currently only getting ~40MPG, which is ~20% below average.
There are two things you might be able to do before you take it to the mechanic, though.
First, run a can of BG44K or SeaFoam through your engine (my suggestion is about a 1/2 a can into a full tank of gas, which is a pretty strong percentage, but shouldn't hurt your engine). This might clean it up some and allow you some better fuel mileage.
The second thing I'd suggest is to try a different fuel brand. Some fuel brands may run well, but just give you crappy fuel mileage. Switching over to a different brand might prove fruitful. I realize on a trip you are really at the mercy of what is available, but still, if you know something is not going to get you good gas mileage, stay away from it.
There is a third, less attractive option ... you could always tow a trailer where you'd keep a jerry can or what have you. You'd almost always have extra fuel in with you doing that ... though I'd bet your travel mates would look at you funny.
Motorcycles usually have a relatively short tank range, typically between 150 and 200 miles to the tank but I had a friend who got 90 miles to the tank on a Honda Hornet 600 so this is still within the range of normality.
The most likely things that are reducing your range are traffic conditions and riding style. Carburettors are quite sensitive to your riding style (more than EFI) so using a lot of throttle will make a big impact on fuel consumption, as will high speed. Similarly, if you're in stop-start or slow moving traffic or you spend a lot of time stuck at the lights you will also lose consume more fuel over the same distance than cruising at a modest speed.
The only likely mechanical fault is that the engine is running rich. This could be because of the carbs not being adjusted correctly or because the air filter is very dirty. However, unmaintained carbs will tend to run lean due to the jets gradually clogging up.