Can't burnout:(

I doubt its the 340 cam its pretty mild, I have it in my 73 dart with a old streetmaster intake and a 600 holley basic 2 1/4 duals off off manifolds with a 2.76 gear. It's not a tire burner but does turn em over easily from a dead stop. Wont burn all the way through first gear like my old roadrunner but modern tires are a hell or alot better. Not knowing what your initial timing is set at I would try advancing it to around 10 degrees or so. Also make sure you are setting timing with vacume advance disconnected. Also dont overlook the ovious. Have somebody sit in the car and hold the gas all the way to the floor and make sure the carb is going wide open and that the secondaries can and are opening. You want to make sure nothing is hanging them up such as a carb gasket either. Also when you change from a 2bbl to 4bbl the kickdown length is all different as is the throtle bracketry, make sure the kickdown is not preventing full throtle on the carb, especially if you are using the one peice kickdown linkage its almost an inch longer.