[Bob KellyIII]

What Jim is saying is just turning on the petcock isn't enough to get gas flowing to the carbs after they've been off and cleaned.... sense it's a vacuum operated petcock they won't get fuel till it's ran a bit.... if the fuel bowls are empty
taking and putting the vacuum line in your mouth and sucking on it and getting gas to the carbs will work ( the vacuum line from the petcock diaphragm) it's a quick cure for empty carbs !
....without doing that you can crank till the battery is dead and it may not fire.... ( takes a long time some times to get enough gas in the carbs with these vacuum petcocks! )

but your using an auxiliary gas tank at the moment so getting gas into the carbs isn't a problem..... I'd use a car battery and jumpers and quick start
to get it going and see if it will actually run... if you don't have quick start use a bit of gas in a squirt bottle ....
if that doesn't work pull the plugs and see if they are wet and if they fire
make sure to keep the spark plugs grounded you can fry the coil if the spark plug falls off the cylinder head and is un grounded.
I just hold them onto the head then hit the start button....
....
Bob.....