Hi, Anthony if your bike has been sitting idle for months or years and you did not do any pre-storage maintenance I feel your pain it will probably have a dead battery and not want to start or if it starts it will idle and run poorly then stall, here are the following steps necessary to complete in order to get your bike back to an acceptable running condition.
1. If your battery was 2-3 years old when you last had the bike running you should replace it.
2. If you believe your battery might still be serviceable remove it from the bike and put it on a 1 or 2 amp trickle charger for 24 hours. If it is the old lead acid type with visible cells and acid levels fill each cell to the top line with distilled water and replace the caps, run the vent tube into a plastic or styrofoam cup, any cells that are cloudy/milky replace the battery.
3. After charging remove the leads and let the battery sit for a couple of hours then check the battery voltage with a volt meter, you should have 12.5 volts or better, any readings in the 11 volt range you need to do a proper load test on the battery and replace as necessary, any readings in the 10 volt range you have a dead cell and the battery needs to be replaced.
4. Drain and flush fuel tank, google " how to clean a motorcycle gas tank" find a couple forums to view the different options available.
5. Remove and inspect your air cleaner paper elements that are not oil soaked can be cleaned with a soft brush and low pressure compressed air, oil soaked elements must be replaced. Gause mesh and foam elements can be cleaned by soaking them in a container big enough to completely cover them with a solution of 1 gallon of water and 1 oz. of Dawn dishwashing liquid for small and medium size elements, for monster size double the formula and let soak for at least one hour then rinse with warm water shake off excess and let air dry, "WARNING" do not use compressed air as this will embed micro-sized dirt and road grime and destroy the mesh pattern and stretch foam elements out of shape just squeeze it like a sponge and let air dry, use a fan if you're in a hurry. When completely dry spray a very fine mist of air filter oil evenly around the whole element.
6. Remove the carburetors, disassemble and decontaminate with a carb dip or if you have EFI remove injectors and clean with carb spray and compressed air
7. Remove fuel valve and filter disassemble and clean as necessary, remove, clean, and inspect fuel and vacuum lines and replace as necessary.
8. Replace spark plugs with new ones and check for spark.
For more information about your issue and valuable "FREE" downloads that you will need please click on the blue links below. Good luck and have a wonderful day.
Suzuki 1200 gsf Bandit problem will not start
Suzuki 2005 GSF1200 Service Manual
OEM parts for Suzuki
Btw, I’m available to help over the phone in case u need at https://www.6ya.com/expert/gregg_c0ec1df182c7330e