welp, you should go through it, someone may have put race springs in it, heavy duty springs..
could be a rusty cable, could be your pinch bolt on the perch is too tight? remove that pinch bolt and check to see if it has a shoulder on it, guys will lose that bolt working on the bike then replace it with a standard bolt which then allows the perch to be pinched onto the lever.. you can kinda tell where its binding, lever, cable or inside clutch just by the feel of it if you been riding a long time..
to check the cable for stiffness, unbolt your lever and remove it.. then remove the clutch carrier case, (sprocket cover) and disconnect the cable from the slave.. then see how free the cable moves, should be very free, if not consider getting a new one or soaking it in evaporust a day or so.. then lubing it well, in any event no point in grinding on it something is amiss..
does it shift and go into neutral OK or can you even pull it all the way in?
if its not the perch, or the cable, inspect the slave.. there are bearings in it that slave that can and will come out so be careful handling it, should be clean and greased, manual should say how many bearings are in it, make sure they're all there and its clean and lubed and nothing is worn excessively like the race and it moves freely...
if the slave checks out then move into the rod that goes from the left side to the right, its slippery, don't grab it with pliers or anything, hit it with a touch of brake cleaner, let it dry then latex gloves it should pull right out..
if not then you need to work it out some way then clean it make sure it's perfectly straight by rolling it on a flat surface, mirror or something..
if the rod checks out then you need to move onto the other side and inspect the clutch, got service manual? could be the springs are toast and they squished up so a rebuild kit is in order, springs, plates, and steels..
do not rearrange order in anyway on those plates, pull the entire pack out as one.. then soak your new in oil overnight, same oil you use in bike.. pretty straightforward just pay strict attention to the direction of everything that comes off, everything, washers, bearings all of it.. maybe video tape and take pics? then the manual shows you how to adjust cable to a tee, may as well go with a new cable if possible, save any future clutch issues if you ride it normally... a dab of grease on both sides of perch and lever..
TM got all the bases. I have this exact bike, and the service manual was a challenge to find online for this exact model but it does exist. Get it, it's free, download it and save it.
What do you mean by "it won't engage"? Like you can't put engine power to the wheel? Or you cannot disengage the clutch when pulling the lever?
The exterior stuff he mentioned like the cable, perch, and pushrod adjuster are all easily accessible, and thus you don't need to be an expert mechanic to check and adjust these things. Start there. If you follow the book and still no dice, then you might want to open the clutch cover.
Also remember these bikes are almost 20 years old. Things wear out. You might need a new clutch cable, a new lever, a new perch, pushrod twist-cam, etc. My 750 when I got it, the clutch did work but it wasn't good. I replaced the lever, cable, pushrod cam, a spring in there, and cleaned the perch and it feels factory fresh again at least in the hand.