yes you can but your pushin your luck. the o.s.77 was very popular when the byron jets come into the public but the f-20 didnt come around till later when other motors were available. but yes i have seen a byron f-20 fly with a o.s.77 and it was ugly but it flew the pilot did nothing but strugle to keep the bird in the air you would be better of with a .91 size motor that has more torque. the f-20 is a good flyer at 10 to 12 pounds. you said your f-20 weighs 16 pounds what all do you have in that jet? you cant put all the bells and wistles in a fan powered model and expect a great flyer.(tryed it with a byron mig-15scale gear,brakes,flaps,speed brakes,canopy opened,landing lightsetc...it flew like a brick not enough thrustwith a rossi 81) a fan model will onlly put out so much thrust so watch the weight if you cant trim some weight,i wouldnt try to fly with a 77 you better put some thought to getting a more powerful powerplant good luck with your project keep em level donnie