This should waken it up. I still use the stock rear spring. The heaviest weights are only 3 grams. Also, a real pipe would help. A motomatic destroyer really awakens these hobbits as well. I also use some cheap taiwan "2k" springs.
If you go to https://www.1977mopeds.com/blog/2009/05/02/polini-cup-may-event/ and click the on demand button, then helmet cam, then twist and go with tommy, you can hear my bike and see what I am talking about. It's a bit gnarlier than most hobbits, but shows you what a hobbit is capable of.