May we have a short tutorial on a section of Mendelssohn Piano Concerto 1 3rd mvt?

Can we have a tutorial on just the section of 3rd movement of Mendelssohn's piano concerto no. 1 in g minor which starts at measure 70(a tempo). I have great difficulty with the repeating 16th note pattern in the right hand that I have heard very young pianists play with ease. My fingers keep locking up after a while, and I can't articulate each note clearly. Of course I have trouble getting up to the speed required for the passage. Thanks in advance.