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2003 CRF450 Jetting Question

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My buddy just bought a '03 CRF450 that has a Pro Circuit 480 kit installed with a Big Bore full system exhaust on it. We went out to Glamis this weekend, and it totally ran like bunk!! Acted like it wasn't getting enough fuel. SO we pulled the needle out and put the clip on the very top position, 7th clip. It ran great once you got it started, but would occasionally die with no reason coming off the throttle and then would not start for about 30 minutes. Got home and pulled the plug and it looked like it had been running very lean. Also pulled the main jet (175) and the slow jet (52). Now, the Big Bore website recommends using a 178 main jet and a stock 42 slow jet. But I dunno with the 480 kit. Anyone have any insight? Thanks.

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