thanks for the reply . I took the FN 49 out today for a test fire. it shot single shot only. The gas port was turned to R I am thinking i need to read up on these rifles a bit more.
Your gas plug is set to fire rifle grenades. Turning it around will allow you to shoot semi-auto. Also, FN-49's have an adjustable gas system. To adjust the gas system, remove the top handguard and you will see a sleeve around the gas tube. turning the sleeve will move it either forward or backward either covering or exposing a gas vent.
To adjust the gas system, turn the sleeve back until the gas vent is fully exposed. Next, load two rounds of the ammo you intend to shoot. Fire one shot and see if the rifle fully cycles. If it does not, turn the adjustment sleeve one click and load two more rounds. Repeat this procedure until your rifle will reliably cycle with your chosen ammo and then replace the top handguard.