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The fuel filters should be full of fuel, check that you can get gas from the tank, if so this means you just need to get the pumps to prime the fuel system and once primed the engines will stay running. This is why when you put gas in the carb the one engine wanted to start or did and stalled because of lack of fuel.
To prime you just keep cranking, I can tell you that is does help to get a little gas in the engine so it starts brifly which helps it prime faster, however you do not want to do this much as there is no oil which is not good for the cylinders.
What you are going through is very common, it is not to say there is not a problem but that they can be hard to start once they sat, check fuel lines are all attached and another problem might be that the carbs/fuel pumps need rebuilt which can happen from sitting.
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