Loris Capirossi says he now suspects that a cracked chassis caused his poor performance and accident in the Qatar Grand Prix.
The Suzuki rider briefly ran second at the start, before losing ground and then crashing out on lap seven.
The accident came as a huge disappointment to Capirossi after he had been highly competitive in pre-season testing.
"I was quick throughout the winter and also in the two days of testing," he told Gazzetta dello Sport
. "Then all of a sudden, since Sunday morning, the bike just wouldn't go, it was unrideable.
"It must have been something with my bike, because (Chris) Vermeulen did not have at all the problems I had. Perhaps there was a small crack in the chassis. The technicians had to verify that."
Capirossi is confident he will fare much better at Motegi – where he has won three times – this weekend.
"Last year I couldn't do anything here because we were too slow," he said. "But now the bike is completely different and I'm convinced I can play for it as I did in Qatar. If I didn't have those problems I would have fought with (Jorge) Lorenzo (for third)."
He also doubts that Casey Stoner and Valentino Rossi will be as dominant in Japan as they were at Losail.
"It's true, they went a lot quicker than everyone else in Qatar, but I don't think history will repeat itself," said Capirossi. "I'm convinced that we'll get closer and I will be at the front too."