If you are restricting air going into the mixer then makes me think that it is a low fuel pressure issue...what parts you use,good quality parts or cheap aftermarket?
On the back of the model j vaporizor is a 1/8 pipe plug....put a gauge in the port and see what your pressure is should be around 1-3 psi
When tou rebuilt the mixer was the bore that the one part rides in was the bore all scored? Is one common problem with that style mixer...the bore gets scored from the valve riding in it and then it hangs up