Normally suspension specialists machine up their own parts to lower suspensions. How many inches are you chasing to lower it?
Generally in the form of washer placed to limit travel.
Are you lowering to be able to touch the ground or trying to lower centre of gravity?
Assuming to be able to touch.
Have you adjusted your rear sag, your owners manual tell you how.
If it is currently set stiff/high you may gain back some distance.
Perhaps use the wheels from small wheel version.
That is what I did when my son was riding a CR80. As he grew the big wheels went back on.
Lower the seat by shaving down the foam might give you enough too. Every little bit helps. Let us know how you go.
C30F Power Up needle
2 turns out
Baffle out, Screens In
It starts,it runs,it gets to where all CRFs can get to without the valve or valve plate dramas