ok so i swapped engines  my original 05 motor blew so i swapped to an 89 motor that my friend had. I have to keep it on prime to run, anyone ever heard of that, or know what i need to do?

I had to keep my petcock on PRI at high speeds due to fuel starvation, which is one of the older GS500's darling quirks....  If you do a search on "fuel starvation," you'll find a number of threads that talk about it.

My solution wasn't really to fix the problem (some members replace their petcocks); I simply ran on PRI during high-speed jaunts, and then put him back on ON while on surface streets and when I was done riding for the day.

My first thought would be to make sure all the vacuum hoses are hooked up correctly.  ie. maybe the petcock isn't getting the vacuum it needs to run in ON or RES