Mount Maunganui's Cody Cooper has made a move up the leader board after the fourth round of the US Motocross Nationals at the weekend.

The former New Zealand champion achieved the best result to date of his Lucas Oil AMA Pro Motocross campaign with a ninth placing at High Point Raceway in Mt Morris, Pennsylvania.

Before he departed to race the 12-round US nationals series, Cooper said he expected the tracks on the East Coast and in the Mid-West would suit his riding style better than the first three rounds on California and Colorado tracks. That proved to be the case in Pennsylvania as Cooper stepped up from being a top-15 rider to post two top-10 results in the 450cc class.

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Cooper qualified ninth fastest and rode his Honda CRF450 to eighth place in the opening moto. He followed up with 10th place in the second moto and his ninth overall was the best effort by a privateer rider. He's now moved up to 10th in the championship standings.

Cooper says practice on his start technique paid dividends at the most recent round.

''I got a lot more riding in between rounds as well and got my bike handling much better,'' Cooper said.

''I still think there is more to come as I didn't feel 100 per cent on track, so I'm looking forward to improving each weekend.''

Kawasaki rider Eli Tomac (US) and Frenchman Marvin Musquin (KTM) shared the wins at Mt Morris, and Tomac continues to lead the championship with 197 points from Musquin on 169.

Round five will be raced at Muddy Creek Raceway in Blountville, Tennessee this weekend.