Where is the rebound adjust on my fork?

[Mudpuppy]

I have a cheap marzocchi that I got on a used bike that I bought mostly complete. It is spraypainted grey and I have no Idea what model it is. It has black plastic adjusters on the top of both legs. I am assuming that they are both preload but I'm not sure.

My problem is that when I bunny hop or do similar things the fork tops out with a vengeance! It makes a loud clunk that annoys me and slightly throws off whatever I am doing from the movement.

I need to adjust the rebound but I don't know where the adjuster is hidden, if the adjuster is internal, or if I'm just out of luck and it's such a cheap model that it doesn't have adjustable rebound. Can someone tell me where the adjustment should be made?

[binary visions]

You've just got a cheap model that doesn't have adjustable rebound. Sorry. Looks like it's time for a new fork :)

[Wumpus]

Pictures are always helpful.

Thicker oil might help. Does it have enough oil?

[binary visions]

If it's got black plastic adjusters, there's a good chance it's an elastomer fork anyway... but as Wumpus said, pictures might help us identify it for you.