I'm making a homebrew with a challenge level of 4 and I don't know what the damage, modifier or reach should be can someone help me out 

(ps it's my first time making a homebrew)

Consult the Creating a Monster section of the DMG: (https://www.dndbeyond.com/sources/dmg/dungeon-masters-workshop#CreatingaMonster), there’s a chart in there and extensive instructions on how to balance a monster’s CR.

thanks for the help

Here is a list of some monstrosities that also bite that are CR 4.  They might give you guidance.

Name          Size

Demogorgon       Medium

Aurumvorax Den Leader Medium

Brown Scavver   Large

Decapus               Large

Girallon Large

Girallon Large

Guardian Wolf    Huge

Kamadan             Large

Thessalhydra      Huge

Yuan-ti Mind Whisperer Medium

Yuan-ti Mind Whisperer Medium

thank you