Is the fuel turned on? That's always a good thing to check
If it's not getting fuel, several things can cause it.
How full is the fuel tank? If the rubber pick-up hose in the tank has rotted off, the fuel may be below the inlet/outlet of the tank and it won't get fuel. A new inlet hose will be required, which has to be installed through the hole in the tank. If this is the case, you will also have to go fishing with a coat hanger for the old hose, as it has a weighted filter on it.
Is the fuel pump working? Remove one of the gas lines from a carb, put the end in a bottle, pull the rope. Is any gas coming out? If not, there may be a problem with the fuel pump. You should get about a teaspoon when you give the rope a good pull. To make this job easeir, remove the plugs. That way, you don't have the compression to pull against.
Next will be inlet needle/seats in the carbs. It would be rare for all three to stick at the same time, but it's possible. If you had really bad gas with a bunch of varnish/debris in it, all the carbs could have gotten clogged at the needle/seat. Not likely, but something to check.