The swapping the carbs trick is a good one but before you do that look in the fuel bowls. There is a wire holding the fuel bowl on the bottom of the carb, each carb. This is called a bail wire (or maybe it's a bale wire). You push the bale wire with a finger, or a screwdriver handle if it's really tight, to one side, it will only go one way and carefully drop the fuel bowl. If there is water in the gas it will be under the gas and you will be able to see it. The water does not mix with the gas. If only gas in in the bowl you can dump this back in the tank. and continue looking for problems. You say that you have put new Bosch coils on the bike. Are these the correct 6 volt coils? Where did you get them? Most parts for Airhead motorcycles are available at some BMW motorcycle dealers. Do you have an Airhead friendly BMW motorcycle dealer near you? Tell us where you live we may be able to suggest somebody or otherwise you will be having to use the postal service and internet ordering. Start making a list you will be having to make an order soon. Put the rubber tubes from the carbs to the heads on your list. You may end up getting complete gasket kits for the carbs or just a few of the pieces but right now you are taking the float bowls off so look at the gasket on the carb body that the floart bowl contacts. So far all you have needed in the way of tools is a couple of metric wrenches and a screwdriver. Start a list of the tools you will be needing. You can get an idea of what tools you'll need from watching the tool kit auctions on Ebay but those too kits are always over priced and few of them are complete. You don't need German wrenches to work on your bike but you may pick up a few. Craftsman Tools from Sears will work fine. Common wrenches needed are 8mm, 10mm, 12mm (need two), 13mm, 17mm, 19mm and 22mm. I'm pretty sure you don't ever need a 15mm or a 16mm, I'm not sure about 14mm. There is a use for a 24mm wrench but you may not need it right away. There are 5 hex key wrenches in the tool kit. Sometimes called Allen wrenches. You need 3mm, 4mm, 5mm, 6mm and 8mm. I really for the life of me don't know what the 3mm one is for but it's in the kit. A metric assortment of Hex Keys will have these sizes and more. You may get by with one of the hex key sets in a holder that keeps the all together and makes it easy to not lose one or two but if you lose any you will lose them all, you know the type I mean. I don't care for those but they are sometimes handy to have and they may be all you find some places. There is a common convertible screwdriver sold in most hardware stores I like. It has interchangeable bits, two sizes for flat and two sizes for Phillips. These seem to fill the bill I think but I usually have others also. I hope that gets you started.