CBR250 RR - doesn't rev when cold

[DaveF]

I'm new here so hi everyone!

I just bought my first bike on Monday - a CBR250 RR '90. Heaps of fun! I've been meaning to get into riding for years and wish I'd taken the plunge earlier now!

Question for you mechanically minded; my bike runs pretty rough when it's cold. It doesn't really rev at all and won't go higher than 8k. Once it warms up it's fine. Even when it's warm though there does seem to be a drop off in power as it goes though 9-10k and then it picks up again, is this some sort of variable valve timing or does that not sound quite right?

Any help appreciated.

Cheers
Dave

[MSTRS:Me]

Sounds to me like your choke system is not working properly. Possibly the main jets are worn or partially blocked. And no doubt the carbs are out of balance, too. A good cleanout and proper adjustment should see you right.

[onearmedbandit]

And no they don't have any variable valve timing.

[DaveF]

Yeah, a bit of an overhaul is on the cards I think. Anyone have an electronic copy of the Haynes CBR manual?

[DaveF]

And no they don't have any variable valve timing.

Wouldn't have thought so. Cheers.

[onearmedbandit]

Have a look here.

[DaveF]

Have a look here.

Useful page thanks. Unfortunately the link to the CBR250 manual is broken. So if anyone else has a CBR250 or 400 manual....

[MSTRS:Me]

Should find it here. Service and maintenance schedules for CBR250RR are downloadable.
http://www.carlsalter.com/motorcycle-manuals.asp

[F5 Dave]

Erm, well go easy on it until it warms up is the most obvious observation.

It could also be a bit lean exacerbating the situation. This could be an emissions thing from std, or non std pipe, or airleak/filter. Or old plugs not wanting to fire under load. Could try raising the needles a notch or small washer, but have to be careful with the diaphragms.