The Fyfe Gambit is a questionable central thrust that has shades of the Center Gambit about it. What difference do the two Knights make to the position?
The first obvious difference is that after 3...exd4 the follow up move from the Center Gambit, 4.c3 is not available. You will have to work hard to eventually win back the pawn. This should be done in conjunction with your development efforts.
Black will not easily be able to play the supporting move ...c5 to shore up his advanced strong point on d4. With the Knight on c6 and the dark square Bishop coming in many lines to c5, you ought to eventually be able to eliminate this problem. This will go a long way to deciding if your gambit has been successful or not.