Topic: Carburetor for 660 cc Engine

[Oette]

Hi guys,

Currently I am thinking of getting a some nice carburetors for my tuned 550 engine.

Some facts:

CB 550 bottom end with 650 crank
A little oversized CB 650 pistons resulting in 660 cc
Ported 650 head
Early style CB 750 carbs with stacks
11:1 compression ratio
Hot Cam with 9mm lift
Electronic ignition with CBR coils

The bike is running pretty good on early style CB 750 28mm carbs and reaches its power peak at about 10.400 rpm (limiter set to 10.500 rpm).
From my point of view the engine has some more potential with adequate/state of the art carburetion.

I discussed the topic with some sohc-people around here in Germany, most of them owning 750's. As the dyno shows the best choice for a 750 may be a Mikuni TMR 32 which unfortunately would be much to big for my 660 engine and is not available in smaller sizes.
Second choice is the Keihin CR series, running 29ers or 31ers on their stock/mildly tuned 750s.

After some more research on that topic I feel like the CR 29 would be the best option to get the performance the engine is prepared to deliver.
Since there is a certain amount of money to spend on a new set of CR 29, I'd like you to share your experiences / opinions with me, especially if you're running a comparable engine type.

Last but not least, the bike is a street bike so I am not interested in losing all my mid-range power to get a short power peak at 11.000 rpm but I am not afraid of a higher mid-range to high-rev power development.



Best regards,

Oette

[turboguzzi]

had 29 Cr in my 500/4 racer, worked really well, would say that's a good size IMHO for a highly tuned street bike like yours. They actually worked very well on my 75/810 kawasaki racer. would say these are 1 st choice rather than second

be sure to add a remote idle adjuster as idle speed tends to vary a lot in stoplights/city riding.

32, specially TMR indeed too big.  just as a comparison, people used 32-33 in tuned 1000cc motors....

[bwaller]

Agreed, to be "suitably steetable" no larger than 29mm.

[Oette]

Thank you for your tips. It's not easy to source those carbs for a reasonable price here in Germany so I am also looking for 'cheap' American dealers to evaluate an import.
Any tips left on that topic?

Best regards,

Oette