If you are running 6G FCAW with an open root there must be a welding procedure specification.
You haven't told us if your even running gas shielded or self shielded FCAW so helping with machine settings is impossible.
Are you in school?...... If yes.. What instructions did you get from your instructor about this project?... Tell us about those and then you can get further tips.
Prolly save alot of money practicing on plate first... It's alot easier to bevel