almost there, carb problems?

[deathcomesarippin]

After my bike sat for 2 years, I pulled off the carbs and had the old man take them to work so he could use some of his tools to clean them out really good. I know they are cleaned out good and they are getting fuel, when I cover them with my hand I feel a good suction and gas is getting on my hand. I've been playing with the mixture screw and I found a good spot, that when I crank it rumbles, but it wont get any further. It starts up for a little with carb cleaner sprayed down the carbs. And just awhile ago while turning it over it backfired really hard and loud, sounded like a gun, its done that three times, and the last time it did I stoped cranking it and took the keys out and then BANG! ... So what do you guys think, replacing those tubes under the carbs? maybe seafoam in the carbs? I could use some good help.