Questions on carb sizing and available options?

Hi all, as you may or may not know i've recently added a new pipe to my pegaso 650 engined rs 125, and got the power up to nearly 48 hp at the back wheel.


I suspect I may be running into the top limit of what the 2x mikuni bst 33 cv carbs I have are capable of supporting, and I'd like to take this engine over 50 hp if I can, with some valve work and a boost in compression and some work on the induction side.

First of all, am I right in thinking I should change the carb to something that would flow a little more air?

And If I do, what should I change them to? My current thinking is to change to a flat slide type carb of the same diameter (33mm) as this matches the rest of my induct and as such would be easier to install.

The only problem is that the only carbs I looked into so far are the keihin fcr's and these would be around £600 for the pair new.... so I'm wondering if anybody knows if anything like these has been used on a production bike that I could pick up cheaper, and if so which bike?

Lastly, my understanding is that the flow rate difference between cv and flatslides is mostly due to the butterfly in the cv? If I'm right, has anybody experimented with slimming down the butterfly spindle, and how much of an increase in flow could you expect from doing this?

Lots of questions I know, but would appreciate the benefit of peoples experience with these carbs as I have very little!

Cheers for any advice you guys may have.

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