Valentino Rossi says the return to 1000cc engines in 2012 could persuade him to extend his career in MotoGP.
Seven-time champion Rossi has hinted his long-term future lies in rallying but, at 2010's first test session, he said he was still hungry for MotoGP.
"I am very happy to go back to the 1000cc because I like it more than 800cc and it is more fun," he said.
"It's an important challenge as far as my motivation is concerned and may convince me to stay in MotoGP longer."
But Rossi, 30, who has one year left on his current contract with the Fiat Yamaha team, revealed he was less enthusiastic about the rules on the number of engines riders are allowed to use.
From 2010 onwards, riders are restricted to six engines per season as a cost-cutting measure, similar to those introduced in Formula 1.
"I think it will be a difficult rule for everybody because just six engines for one season is not enough, it is very tight," said Rossi.
"If we have eight or 10 it is easier and less risky."
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The Italian was speaking at the first MotoGP testing session of 2010, at Sepang in Malaysia.
And he showed his title-winning form of last year has not deserted him as he topped the time sheets with a fastest lap of two minutes 01.411 seconds, just one second off the time which earned him pole position in the Malaysian Grand Prix last year.
Ducati rider Casey Stoner, who finished third behind Rossi last season after an illness-wrecked year, was just 0.491 seconds slower, with Tech 3 Yamaha rider Colin Edwards third fastest.
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