yes you need to run a spacer (it goes behind the counter shaft sprocket) I bought one from Fastway they are located in Portland Oregon they sell quite a few trick parts for CRF's the spacer is less than 2.00 you'll have to look them up I don't remember the site.
Go to your local autoparts store or engine shop and get a 60 thousandths valve shim with 1"id. It fits perfect. It'll probably cost you a quarter. My local napa store only had 15s in stock so I got 4 of them, he gave them to me. Ended up stacking 3 together & it was enough to clear the case.