78 KZ750 strange noise on take off... clutch?

Hey all,

I've been riding and sorting through details on the kz750 twin I picked up in march. I've put a little over 4k miles on it so far. Mostly riding to work and back, but longer weekend trips in the Adirondacks and Catskills and Vermont as well. So far the bike has never let me down, and it rides and starts beautifully... and gets lots of comments everywhere I go as well. I really like the torque happy twin - really useful every day kind of bike, in my opinion.

Since I've had it I've taken out the starter clutch (was in immaculate condition) and added the locktite I've seen recommended. I've also changed the oil and filter, new plugs, new fuel lines and filters and bumped the counter shaft sprocket up a tooth as well. Like I said it runs beautifully.

My one concern: In the past couple weeks of driving to work I've started getting a weird noise when accelerating from a stop. It's almost a "grinding" noise, like metal on metal, and it's coming from down below. It freaked me out a lot the first time, but it's infrequent and I can usually keep if from happening by starting off gently. I've never heard the noise once I'm out of first gear, and it shifts up and down great and the clutch feels fine. I'm not 100% certain on when I first heard it, but if I had to guess I think it was some time after I changed the sprocket... which was also when I changed the oil (to Amsoil motorcycle). I'm not sure if either of those things could be related - I drove it a few days after that before I remember hearing the noise - but I don't know what else to suspect. Does this sound like a clutch thing? Something else? Like I said the noise sounds kind of bad... but It works great otherwise and I can pretty much keep it from happening. I'm planning on taking a 2.5k mile trip down south on the bike in a few months though... and if this is a real problem I'd like to fix it now, while I have a chance! Anybody have any ideas? My one other whim was that it could possibly be valve related? But I don't know that much about those to know if that could even cause a sound like that. I have the head cover gasket and have been planning on checking the valves as a maintenance thing anyways - I doubt they've been checked ever in the bikes 20k miles, but like I said it seems to run great....

At any rate, any advice would be appreciated, thanks!

My moneys on the new larger counter shaft sproket is grinding the chain into a cover.
Open her up and have a peek.

i will 2nd that

also the chain might be loosen up after new sprocket break in

I will 3rd that
also check the front sprocket guard is not loose or rubbing the chain
original 16T



With 17T



Good Luck,
Jim