Chris Walker has turned down an improved offer from Foggy Petronas and will race instead for the Kawasaki PSG-1 team in next season's WSB championship.
The Nottingham rider was the first to secure a podium finish for Foggy Petronas in 2004's first race at Valencia.
FPR team boss Carl Fogarty said: "Every rider likes to have their own mechanic with them, as I always did. So we put together an attractive package, which included the addition of his mechanic to our team. However, circumstances beyond the control of all those involved, meant that Chris wasn't able to accept that package.
"We were confident that, after a season of adapting to our triple, Chris would have been able to fulfill his potential and become a consistent front-runner next season on the FP1.
"Chris has enjoyed most of his success in the past on a four-cylinder bike and probably feels that he is more at home on a Kawasaki. But we are sure that the PETRONAS engine development team will make big strides forward during our winter testing programme and that our bike, which we know is fast enough to achieve pole positions, will be able to challenge the established manufacturers on a regular basis."
Walker said: "It has been a really hard decision as I have really enjoyed my time with the team - and Foggy has been a star. But the timing is right for me to get back on a four-cylinder."
Walker was 11th in the rider standings this season, with 128 points.
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