Keihin FCR vs CRS

ivar

ivar

TT Racer
Main differences are CR = round slide, FCR = flat slide, and CR's used on these bikes are 35mm diam, the FCR's are 39. (and the price is a bit different too..,)
 
zmilin

zmilin

Street Tracker
cool!
So both are available in 39mm bores.

What is the benefit to a flat slide vs a round slide?
 
Dave

Dave

Street Tracker
I'm not sure, but I think the flat slides are cable actuated and the rounds are vacuum actuated, the flat slides have quicker response time
 
ivar

ivar

TT Racer
The roundslide CR's are also cable actuated. The vacuum operated are also called Constant velocity (CV) carbs.

From what I've heard, one of the benefits of flatslides are shorter distance from cyl to needle/jets , resulting in stronger carb signal and better fuel atomization....?

One other benefit of flats is that they are usually racked together, causing them to stay better in sync and requiring less effort to open.
 
sweatmachine

sweatmachine

moped
zmilin said:
For those of you in the know...whats the diff between FCR and CRS carbs?
Click to expand...

I wouldn't waste my time on CR carbs.

The CRs are 35mm
The FCRs are 39mm

FCRs are flatslides with accelerator pumps. The CRs are roundslides with no pumps. The pumps help big carbs respond better to whacking the throttle open to eliminate bogging at low rpms. They really do work well.

You will get more hp, torque, and throttle response with the FCRs.
 
zmilin

zmilin

Street Tracker
Keihin web site shows the CRS are available up to 39mm. I guess I shouldn't assume that that will fit our bikes.

Bottom line seems to be throttle response due to cable vs vacuum.

Thank you all for the input!
 
You must log in or register to reply here.
Top