Suzuki GSX-R Motorcycle Forums Gixxer.com banner

1 - 11 of 11 Posts

·
Registered
Joined
·
1,014 Posts
Discussion Starter #1
They give more H.P. They don't work on vacume so the throttle response is quicker. The downside is they are not as smooth as CV carbs for the street.
IMO they are worth it.
 

·
YAAFM Mod
Joined
·
3,016 Posts
On your stock CV carbs the throttle is not directly connected to the slides, when you open the throttle it uses vac at the diaphram to open the slides. so they open slowly but smoothly. A "flatslide" carb (mikuni or keihin) the throttle cable is directly conected to the slide so they open quickly and they also have better flow due to less restrictive venturi's.
The main difference between the Mikuni RS carbs and the Keihin FCR's is the slides in the FCR's has roller bearings for the slides to make them smoother, the slides in the the RS's have a tendency to drag when closing at high RPM when the slides drag against the carb body.
Bones
Bones
 

·
Registered
Joined
·
463 Posts
Thanks guys...and Happy Birthday Bones.
Can you tell me how long these CV carbs last? There must be a lot of wear on these slides because they are moving up and down about 5000 times per minute and all this without any lubrication.
I read the post "desperately seeking flatslides" and learned there that 36mm flatslides are equivalent to 38mm CVs. That makes me wonder why the 1127s equiped with 40mm CVs are not more powerful than the ones with 36mm CVs, according to "Performance Bike" magazine.
 

·
YAAFM Mod
Joined
·
3,016 Posts
If you look at the specs for a 91-92 Euro 1127 with the 40mm CV's you will see that the 91-92 dropped compression from the 90. They changed the cam profile too with the switch to shim under bucket adjusters. This happened to the US models too. They seem to last awhile but if looking for some 38CV's or 40's look for low miles they are out there.
Bones
 

·
Registered
Joined
·
3,895 Posts
Originally posted by Wolf1100L:
Thanks guys...and Happy Birthday Bones.
Can you tell me how long these CV carbs last? There must be a lot of wear on these slides because they are moving up and down about 5000 times per minute and all this without any lubrication.
I read the post "desperately seeking flatslides" and learned there that 36mm flatslides are equivalent to 38mm CVs. That makes me wonder why the 1127s equiped with 40mm CVs are not more powerful than the ones with 36mm CVs, according to "Performance Bike" magazine.
<font size="2" face="Verdana, Arial">I'd also suspect that the extra mm's on the carbs doesn't matter much with the stock exhaust in place... gotta move more air outta da motor to move more in.
 

·
Premium Member
Joined
·
3,306 Posts
The slides aren't moving up and down 5000 times/min. On a CV carb when you open the throttle the slides move up, but how quickly and how much is dependent on the airflow through the carb. Open the throttle, it opens a butterfly and lets more air in. The increased airflow draws more fuel in, the engine rpms rise drawing more air and fuel in. As the revs increase drawing more air in, the slides continue to rise, letting more air and fuel in and so on. The slides rise and fall smoothly with the throttle but aren't tied directly to the throttle cable like flatslides. A flatslide carb can be opened fully at low rpms and the engine can bog because there is a big hole and the engine isn't flowing enough air to draw the fuel in, even with accelerator pumps. Flatslides make bigger hp but need a smooth hand at low revs.
 

·
Registered
Joined
·
3,895 Posts
Originally posted by 341:
The slides aren't moving up and down 5000 times/min. On a CV carb when you open the throttle the slides move up, but how quickly and how much is dependent on the airflow through the carb. Open the throttle, it opens a butterfly and lets more air in. The increased airflow draws more fuel in, the engine rpms rise drawing more air and fuel in. As the revs increase drawing more air in, the slides continue to rise, letting more air and fuel in and so on. The slides rise and fall smoothly with the throttle but aren't tied directly to the throttle cable like flatslides. A flatslide carb can be opened fully at low rpms and the engine can bog because there is a big hole and the engine isn't flowing enough air to draw the fuel in, even with accelerator pumps. Flatslides make bigger hp but need a smooth hand at low revs.
<font size="2" face="Verdana, Arial">That's kinda true re: the CV's... They are not directly tied to the throttle cable, but they do cycle up and down quite a bit... at WOT the slides are stuck wide open... but from just off-idle through intermediate RPM's and throttle-position, the slides actually rise and fall a fair amount with each pulse of intake-charge that flows through them. They open more and close less with rising RPM's/throttle-opening, and no, they do not cycle fully-closed to fully-open with each intake stroke, but they definitely hop up and down a lot, not like the smoothbores/flatslides at all. That's the big reason why the emulsion-tubes and slides get worn-out and sloppy.
 

·
Registered
Joined
·
553 Posts
Fastcat,

First, Happy Birthday....have a good one..!!

Second, I know you just rebuilt your CV's recently. Did you use any kind of lubrication on the slides, or just cleam them up and let them run plastic on plastic..??

Thanks....Dave.
 

·
Registered
Joined
·
434 Posts
another diff is the flatslide does not have a throttle butterfly in the venturi so at wide open throttle there is no restriction like there is in a cv carb with the second throttle plate in the venturi which disrupts the flow a lot.
 

·
Registered
Joined
·
3,895 Posts
Originally posted by davenay67:
Fastcat,

First, Happy Birthday....have a good one..!!

Second, I know you just rebuilt your CV's recently. Did you use any kind of lubrication on the slides, or just cleam them up and let them run plastic on plastic..??

Thanks....Dave.
<font size="2" face="Verdana, Arial">No lube... I think fuel tends to kinda lube em while in use... it would definitely wipe out any kinda grease I put in there. I *did* put new slides in though, along with the emulsion tubes. The slides are ~$35 ea. and emulsion tubes are ~$12 ea from Ron Ayers if I remember correctly. New slides do not include the diaphragm.
 
1 - 11 of 11 Posts
Top