08 450F - Big Bore Jetting & other questions

Ok, so I just put in the Cylinderworks 480 kit (with +3mm Vertex piston).

Seemed to be running very lean, so I've re-jetting a few times already.

Now I'm at 5000ft high desert, 90 deg, 48p, 175m and the Half-step richer needle in stock clip position and 2 turn out on Fuel screw, O-ring trick in place, and everything else is stock.

Seems about 95% good now, seems to have either a cough, bog, or surge at 1/8th to 3/8th throttle. I can't really tell which, but something wierd happens around there every now and again.

So anyhow, do you usually have to go so big on the jetting with a big bore on these bikes?

Any other tips or tricks when going the big bore route on 4-strokes? I'm considering bigger and stroker next time as well. I can see a bit more power that I like so far!

Thanks in advance for your comments!


I'm still at 48p, 175m but I put the stock needle and dropped the clip 1 position (richer) and down to 1.5 turn out on Fuel screw.

Seems much better, it had some hesitation or blubber at 1/8 to 3/8.

It did cough once on my last ride around that area of throttle, and only after either:

1) Chopping the throttle off on (due to corner or whatever obstacle coming)

2) Hitting a section of whoops then chopping the throttle on - off again

Other ideas?

It's actually really good now, and I'm calling this my YZF 505 (since it's really the same size engine as the KTM 505)! :smirk:

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