I didnt say it COLDNT be done...
but a 4" neck can only take so much air, certainly not the 90scfh the askoll 1500 is capable of producing...65 scfh maybe...but the more air, the harder to control too.
have you tested your pump with an air meter to see what it draws??
I think luke does it, but with an extended neck and is only getting 65scfh.