Can't fill up

Have this same problem with my '66 Valiant. If I put the nozzle in the filler neck normally I can only get a half tank in before gas starts running all over the place. If I put the nozzle in the filler neck upside down I can fill the tank completely. Don't know what causes this but it works for me. It's just a PITA to use my thumb to squeeze the handle. Hope this helps and why don't you try it and let us know how it works for you.