"I'll be a little disappointed if I don't finish among the top 10 this weekend," said 20-year-old Ainsworth.
"I know I can run the pace to be up there, especially around Harrisville. I've been racing at this track since I was about 8, so that's a few years now.
"Getting a good start is really important at Harrisville.
"Fast lines form on the inside of corners and it gets quite rutted, then gets hard-packed late in the day. I will really need to be on the ball."
O'Connor, McNeil, Dragt and Trappitt all race in the 125cc class and they are positioned eighth, 14th, 22nd and 24th respectively after two rounds.
Trappitt did not race at round one near Timaru, so his catch-up mission is even tougher than most.
Cooksley races in the non-championship MX3 class.
Pukekohe club rider Kurtis Lilly will not be in action after hurting himself in the second round near Morrinsville a fortnight ago.
Racing at Harrisville on Sunday begins at 10am. The series wraps up in Taupo on March 31.