'81 CB900 - CR31 or CR33s? advice please

Hi Everyone,

Just after some advice if anyone has had any experience - I'm rebuilding my old '81 CB900 and so far in terms of engine modifications just putting on an aftermarket exhaust. I may in the future decide to bore it, put in some wiesco pistons and drop a hot cam in too but at this point haven't decided.

I'm getting a new carb and am unsure on whether to get the CR31s or 33s - I have heard some reports that the CR31s can run out of puff pretty quickly once you start upping the power on the bike, but I'm unsure whether the CR33s may be too big for my application.

thoguhts/advice?

Smaller better. If you are regularly riding such that you could tell the difference your next bike will be MotoGP.


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I've heard a pretty common upgrade for road use was to put 750 carbs on the 900's. This boosted low end and mid range power with the slightly smaller carbs.


Let's face it - no one rides an 80's superbike at WOT all the time on the street.

fair calls - unless anyone has some alternative advice the CR31s sound like the go then

Thanks guys

CR31 will support around 35~ 50bhp per cylinder depending on how efficient intake/exhaust tuning is.