Hi fisherjay, from what you describe could be many things, we had a similar problem, my advice is as other people have suggested, you need to pinpoint exactly where the problem is, is it the cables or is it at the gearbox, take cowling off & check cable movement both in forward & reverse, watch the linkages & make sure they are moving roughly the same distance in each direction, if you think this is fine then disconnect cables rom linkages & try & put into for/rev manually, spinning the prop so you know its engaged, if it goes into gear this way you know the problem is in you cables or throttle box, if it doesnt go into gear manually the problem will be in your leg linkage or dog clutch.which if your not mechanically minded is a job for huey, we had to strip ours right down & the pin in the middle of our dogclutch had a little crack in it & was bent slightly but this was enough to stop it going into reverse as the dogclutch is springloaded but only underload when in reverse not forward, also. whilst it sort of half went into reverse & this did spin the prop with the muffs on when we held some rubber against the prop you could hold the prop so we new the gear wasn,t engaged fully.
Don,t know if this all makes sense but basically identify if its cable related or gearbox end first.
Rod