WR390 fork adjustment

Hi, I have put together a pretty nice WR390, it runs and rides amazing for the most part, however I am curious about an issue with the forks, when I do a wheelie and the front tire comes off the ground there is a noticeable clunk in the forks as they reach their full extension. Is this normal? I am going to change the fork oil and see if that fixes things but is there something else I should be looking at? As far as I can tell its stock and in good condition, there is no binding or other issues.
Thanks

Nothing I do seems to allow me to post a picture to this site and have it the right way up...not sure what that is all about. View attachment 104840 for your help and Ive attached a pic of the bike.

1. The rings at the top of the dampening rods are worn out or broken
2. You are using fork oil that is to light of wt.
3. not enough oil in the forks.

Marty

THanks, Ill look into those things. Are the damping rod rings still available ?

Available from HVA-factory.com, Racetech and some other vintage suppliers. Referred to as several different names: fork piston bands, top out washers, damping rod washers as well damping rod rings or piston rings...

While you're in there, clean the INSIDE of those chrome tubes as good as you can. They were very poorly finished from the factory, often rough and rusty. That is why the lifespan on these rings is often not so good. The newer rings all seem to be made from better plastic, too.