2003 CRF450 Jetting help

[liquidthumper]

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.

?

[toolpro]

Put the needle back to the stock position put in the 178 main and fuel screw out 1 1/2 see if it is better. Is the head ported? If this does not work check the accelerator diaprahm. Change the accelerator stuff three times a year. Good luck.

[James_Dean]

My guess is to use the middle clip position and lower the main jet to a #170.

The top clip position was far too lean, causing stalling, but may have helped at full throttle where the bike was rich before.

The #52 pilot jet is too rich in most cases. The bike should have a #45 (or #42) to be in the normal range at idle. This also could be the source of hard starting when hot. As mentioned, start with the fuel screw at about 1 1/2 turns out.

James