I have a Diamondback frame I'm guessing around 1984 or 85 serial # F4042789
Check out this thread, the bike in question matches "F4042" S/N portion with yours. According to messages, your bike was built by Formosa in Taiwan (F) in 1984 (4), so it's not Formula One, which was made in Japan. This post mentions that "Viper, Pacer 500 & Super Streak were available that year", but an archived copy of os-db reveals there were also Harry Leary, Super Streak, Super Viper and Viper.
To narrow the options down further, you can:
- Visit all links above and see what matches your bike features the most.
- Post photos here, especially serial number, dropouts, rear brake bridge. Full side shot would be good too.
I'm inclined to believe it's a 1984 Super Streak because 5 out of 8 serial number symbols match.