[pnj]

I have a dirt jumper 2 fork from '02 or so. It's currently at 100mm. I would like to drop it down to 70-80 and eventually set up a 24 inch bike.

what do I need to do to drop this fork?

 

[BikeMike]

Probably just need some spacer and oil.
If you pull the cartridges out I think they'll be the straight SSV if you have the DJII or SSVF if you've got DJIs. Place a spacer so that the negative travel spring is effectively taller. You can also use an additional negative travel spring for this, if you have one lying about. Possible also that you will have one or two spacers that can be swapped from the positive travel spring side to the negative side. Otherwise, just improvise with suitable piece of pipe. If you didn't remove any spacers from the positive travel side (big long spring side), you can either cut your main spring (a PITA, and won't have the right coil at the cut end, which at least has the potential to cause grief), find one that's the correct size (often $$$), or, if it's not too drastic a travel change (100-->80mm should work fine), just cram it back in (will have increased pre-load, but shouldn't be a biggie with the likely application).

The oil is to re-fill when you put it back together.