helicoil is the best way, but you may be able to JB weld it, fill the hole with JB and then screw in a bolt that is longer than the stud was (cut off the head of the bolt before screwing it into the JB Weld filled hole) then put your head pipe on and use a nut on the bolt you put in. dont be aggressive with tightening it, a little at a time so it doesnt spin in the JB W. also make sure to give it plenty of time to cure up good.
TRIKES....BADDD ASSS BIKES!!
1986 200x
1995 300ex
2000 400ex
1989 CR80
1996 CR 250R
1997 XR 70
1977 YAMAHA XS500
1989 KITTY CAT