Hey there,
Im looking at a yamaha yzf600 bike (2003) with 1,500 miles on it. I test rode it today and the only wierd thing about it was that under heavy braking the front end made a sort clunk as it dived. Now i don't know if this was normal or not but i do know the suspension was set at pretty soft (female owner).

Anybody have any suggestions or comments on this or the bike itself?

Thanks

Might be a play in the steering head bearings.Easy to check.Grip both fork sliders and try to move them forward and backward,if you hear clicking as you described and feel slight movement then steering head bearings need adjustment,just like on the GS.

new fork oil and seals maybe?  I dunno... suspension is out of my ballpark

You should be able to check these things, but not without being obvious.  If it's front fork related, then pushing hard on the front end should reproduce this.  If you bottomed out on hard braking, it should also be obvious.  Push-Pull the front wheel to check the head bearings -- shouldn't be more than mild movement (~1/4 inch or tighter).

If the front end is soft, you have full adjustments to play with.

My '02 GS did the same thing (and had since the day I got it) when I hit a transition to a driveway etc. from the street, until I put in progressive springs. I don't think that I heard it in breaking, but it was a pronounced clunk. I used to check the nuts on the head and never noticed that they were loose, so I alvays figured that it was weak stock springs that were just compressing too quickly. It went away when I upgraded springs.

I was never able to recreate the sound by forcing the front end down manually, it only happened when I bumped the wheel up while riding.

such a new bike with little mileage, I'd guess the steering head was never readjusted after purchase (should be checked after 600 miles). as mentioned above, you should be able to recreate movement in the forks, but if you cant they might still be loose, just not loose enough to move by hand.

if its at market rate insist to have it checked by a yamaha dealer. if its well below market probably okay to buy as is.

I own an 01 YZF and its a great bike. One of the best do-it-all bikes you can find. 

The suspension is very sensitive to adjustment. If she had the preload and compression damping backed off then the forks could have been bottoming out.  Its possible that the steering head was loose (unlikely that the bearings would be bad on that young a bike), its been known to happen, especally if it was neglected during after break-in services. You should be able to eyeball the steering stem nut and see if its finger loose. Also you could take another test ride and try and tighten up the preload and tune out the dive.

Since you haven't bought the bike, its understandable that this is giving you pause. But it doesn't sound to me thats a serious problem, though you could use it to try to quibble the price down a bit.