It is probably too lean.
Have you opened up the needle valve?
Or:
Disconnect the fuel line from the carburetor and connect about one foot of fuel line. hold this fuel line below the tank and watch the fuel flow. It should siphon out of the tank at the rate of 1 or 2 ounces per minute. If it does not, then something is clogging it - perhaps a kink in the line inside the tank.
If the fuel flow is fine from the tank, then it is clogged in the needle valve area. remove the needle valve and blow fuel thru this area. you can just pump fuel into the normal nipple that goes into the carb and fuel will spurt out from the hole where the NV used to be.
Also, get the engine started at idle, then begin to open the throttle watch carefully for bubbles in the fuel line. I know you said you changed the fuel lines, but this is an easy test to run. if there are bubbles in the fuel line the engines tend to go lean in the air and quit.
Finally, sometimes air can leak around the NV or where the carb is attached to the front intake. Try to check for air leaks in this area.