Both of these guys are dead on.
I always run 7 degrees and about 1/8 of a inch toe in.
When I first got my 32 roadster back on the highway in the late 80's ... I had a similar issue. I reset the front end to 7 degrees king pin lay back and 1/8 inch toe in and the issue disappeared.
Also too wide a tire on the front can cause problems. A rim with a lot of offset can also aggravate the issue.
Now both of my 32's rim a fairly small front tire with almost zero offset on the rims. Not a problem with either one ... over 50 thousand miles on the roadster and one summer on the 3W.