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Discussion Starter #1
So, I thought I'd ask the question as to why carbs such as keihin FCR's are considered better than standard carbs?

What are the pro's and cons?

:idunno:

As an aside - I run a 94 CBR900RRR - so if I was considering FCR's - which ones should I go for ? And why?

Thanks in advance.....
 

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So, I thought I'd ask the question as to why carbs such as keihin FCR's are considered better than standard carbs?

What are the pro's and cons?

:idunno:

As an aside - I run a 94 CBR900RRR - so if I was considering FCR's - which ones should I go for ? And why?

Thanks in advance.....
Great question Saxy (not to be confused with sexy):eek::rotfl:


So to maximize fuel mix and giving a Carbed bike about all it can handle this side of a turbo, a Kehin flat slide carb (FCR) is the ultimate intake upgrade for a normally aspirated Carbed engine. Now, let's not get too hung up on the term "flatslide" too much. If you've been into your carbs (and I'm sure you have), you'll notice that Hey, the slide is flat! What gives? Well, you'll also notice that there is the Constant Velicity diaphragm attached to it as well. That fact, in conjunction with the butterfly valves are what separate a set of FCR's to stock. There's no vacuum regulation as to how fast the slides lift on an FCR.

An FCR has a direct activated slide on rollers. When you twist the throttle pipe on the FCR's you're raising the slides mechanically, directly. Opening up a basically unobstructed path for the mix to get burned. Here's a couple pics. Slim body, just big enough to hold the giant slide:



The slide with rollers:



And under the top cover (no diaphragm):



They are GREAT for racing applications. That being said, they have a myriad of adjustments. Needle length, needle taper, beginning of taper, mains, pilots, idle, and syncing can be chore. They are also very hard to dial in for road applications, and don't like small throttle openings at low speeds, hence drivability can suffer greatly. Also, getting them to idle smoothly is work. However once they do get dialed in, especially at idle they sound amazing as the slides rattle like crazy and make the bike sound vicious!

They can also sometimes present a much "heavier" feel on the throttle pipe, as you're not turning week sprung butterflies anymore, but 4 mechanical slides.

Also, there is no "choke" on these carbs. They do have an "accelerator pump", which when you "whack" the throttle prior to starting squirts a bit of fuel to help a cold start.

Your 94 900RR carbs are 38mm (bore). The FCR's come in 39mm and 41mm, but unless your engine is built to the hilt the 41's won't make any difference. 39's are the way to go. Mikeo has a set on his killer 93RR race bike. I'm sure he can give a more "seat of the pants" tutorial on them.

I hope that helps explain it a bit:thumb:
 

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Great explanation Ian, no longer a carb guy, but you answered some questions I've had for years and never researched. Not to mention you never know when an interesting carbed bike may come along for sale.
 

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Great explanation Ian, no longer a carb guy, but you answered some questions I've had for years and never researched. Not to mention you never know when an interesting carbed bike may come along for sale.
Thanks fj, I forgot to say that just owning a set is pretty balls awesome:D

They look as good as they sound:



On a YZF:

 

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Discussion Starter #6
But sounds like if using a road bike for road use, stay with standard carbs... Despite the awesome looks and sounds of FCR's...
 

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Ian - awesome explanation. Thank you.
My Pleasure:thumb:

But sounds like if using a road bike for road use, stay with standard carbs... Despite the awesome looks and sounds of FCR's...
Yes, at the end of the day FCR's for road use can become much more troublesome than their worth. I kept my OEM carbs on my original 1024cc 93 build mainly due to wanting to keep my street drive ability. BUT, my friend had them on his street built FZR1000 and rarely had an issue, on the other hand that picture of them on the YZF, that buddy had problems with his starting, idling, everyday running, and was constantly changing settings just to get it to run.

It's a hefty investment to end up "not liking them".
 

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Discussion Starter #8
I think I will just install a dynojet kit and k&n filter when I finally refresh the bike (shame - liked the looks of the FCR's :evilaugh:)....

Thanks again....
 

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Discussion Starter #9
So...I see in Mikeo's thread that he has a powerpak...

Got me to thinking what real world road benefit is gained from such equipment, and whether they are worth investing in for a 94 carbed blade?
 

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So...I see in Mikeo's thread that he has a powerpak...

Got me to thinking what real world road benefit is gained from such equipment, and whether they are worth investing in for a 94 carbed blade?
The V&H PowerPak was pretty trick stuff back in the day, and really only came down to being a semi-programmable ignition curve/rev limiter. However, if one was left at my doorstep I would surely plug it right in. Trying to find one of them would be very hard IMO. They were pretty cool to have though:eyebrows:

Here's a description:

"A direct descendant of our race team's on-board engine management systems, the PowerPak is designed for the street rider and racer alike, who wants the maximum performance possible for a fraction of the cost. The revolutionary POWERPAK is a device that allows the rider/tuner to select between sixteen different combinations of ignition timing and rev-limit, from stock to as high as 14,000 r.p.m. depending on the specific engine combination or riding application. The rider has the option to use an economical, near-stock setting for everyday use, or with the flick of a switch, select three higher performance ranges. The ignition timing is fully mapped from 2000 r.p.m. to 14800 r.p.m. Included in the circuitry is a fully digital 80c51 microcontroller chip running at 12 megahertz clock speed. This means unmatched accuracy to within 1 r.p.m. All this comes in a machined billet aluminum case that simply replaces the stock ignition black box. Truly the most innovative performance part available at any price, the PowerPak comes with a complete user manual and installs in minutes."
 

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Discussion Starter #12
But.... I have never felt the need for more top end speed, but can always use a little more real world traffic light torque and and overtake get up and go.......
 

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Discussion Starter #13 (Edited)
Here is my 94rrr with some minor mods...

Now considering a refresh (and investigating possible appropriate tweaks)....

(Apologies for low res photo)....
 

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Wow!!!!! If you want it I would send him an offer. That's something to have, but for some better get up and go if you haven't already, try for a low end gearing change. The 900's always had a nice low and midrange grunt, but were never horsepower whores. The SRAD GSXR 750 made just about the same horsepower when it came out, unless you heavily modify the engine, you'll be chasing HP like the initial high from heroin (forever). I had 5mm over Pistons, ported head, Carrillo rods, degreed cams, airbox kit, albeit stock carbs, but I spent like 5 grand on just motor mods, only to get about 135HP at the wheel. If I had gotten the FCR's I probably could have added another 8-10 MAYBE. And nowadays that's nothing.

I loved the driveability of the stock carbs, but always had it in the back of my head whilst doing 160MPH leaned over that something would grenade on me. The bike was quick, but I never changed the gearing. So I was never gonna go any faster that the OEM top speed. Which was always fast enough.

Now, I have a different perspective. I would take a properly running, jetted with pipe 900RR all day long. That's why my red bike stayed stock. It runs great, and there are no questions about reliability.

Sorry for the dissertation, but sometimes I forget to shut up;)
 

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Discussion Starter #15
No no - great post... And happy to read a good response.

Likewise, I am only really interested on reliable and affordable gains..(if I need to spend more money than buying another bike, I would buy another bike)....

No engine work as yet (and none really planned (perhaps new cam chain tensioner)).

I use my bike as a road machine only (limited to 70mph on the roads), so 160mph is more than sufficient for my needs...

But good carburation, no flat spots, low down and midrange torque with nice exhaust growl and air box accompaniment ...... That is a useful aim is it not?

Already have the dynojet / k&n set to install...but waiting till take bike of road to refresh (as I commute on it daily)... And considering the stick coil conversion (have a spare loom to amend so I can keep all original stuff unmolested also)...

Other than than, mods have been for convenience and appeal...

SSSA - changing rear wheel really easy and looks nice too...

CBR1000RR forks with 954 yokes (radial monoblock calipers and mastercylinder, 310 discs, 17" front) - looks nice (and in my opinion behaves better - I know there will be many who may disagree)...

Asv levers (perfect finger span adjustment)...

But at the end of the day... I do not ride hard enough to need a steering damper, and definitely don't use all the power available...

But I do enjoy not having a standard bike (although all the standard bits are mothballed for later use...) so I guess I enjoy the tweaking because one can.....
 

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No no - great post... And happy to read a good response.

Likewise, I am only really interested on reliable and affordable gains..(if I need to spend more money than buying another bike, I would buy another bike)....

No engine work as yet (and none really planned (perhaps new cam chain tensioner)).

I use my bike as a road machine only (limited to 70mph on the roads), so 160mph is more than sufficient for my needs...

But good carburation, no flat spots, low down and midrange torque with nice exhaust growl and air box accompaniment ...... That is a useful aim is it not?. 100% yes, agreed

Already have the dynojet / k&n set to install...but waiting till take bike of road to refresh (as I commute on it daily)... And considering the stick coil conversion (have a spare loom to amend so I can keep all original stuff unmolested also)...

Other than than, mods have been for convenience and appeal...

SSSA - changing rear wheel really easy and looks nice too...

CBR1000RR forks with 954 yokes (radial monoblock calipers and mastercylinder, 310 discs, 17" front) - looks nice (and in my opinion behaves better - I know there will be many who may disagree)...

Asv levers (perfect finger span adjustment)...

But at the end of the day... I do not ride hard enough to need a steering damper, and definitely don't use all the power available...

But I do enjoy not having a standard bike (although all the standard bits are mothballed for later use...) so I guess I enjoy the tweaking because one can.....

Those mods are perfect, dresses her up a bit, AND adds total functionality. BUT, you need to honor her by adding MANY MORE photos:D

These older Carbed 900's are such a treat to work on, their spacious (no cramped quarters full of electronic mucky muck), big beautiful frames, and straight forward motors. I'm glad there's still parts availability, enthusiasm to keep them looking good and a NEED to make each their own:thumb:
 

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Discussion Starter #17 (Edited)
So I have ummed and aahhed and ummed and aahhhed... And then bought and paid for a V&H PowerPak from evilbayusa. . Should arrive from USA in a few weeks....:evilaugh:
 

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Discussion Starter #18 (Edited)
Those mods are perfect, dresses her up a bit, AND adds total functionality. BUT, you need to honor her by adding MANY MORE photos:D

These older Carbed 900's are such a treat to work on, their spacious (no cramped quarters full of electronic mucky muck), big beautiful frames, and straight forward motors. I'm glad there's still parts availability, enthusiasm to keep them looking good and a NEED to make each their own:thumb:
Will add some more photos in due course....:thumb:

Oh - and I like the blade I have... Carbureted.....
 

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Discussion Starter #19 (Edited)
So... Next question ... What's with quick action throttles... Is this a different cam on the throttle grip, or a different cam on the carbs (or both)......?

And what difference does it really make?
 

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So... Next question ... What's with quick action throttles... Is this a different cam on the throttle grip, or a different cam on the carbs (or both)......?

And what difference does it really make?
It can actually be a series of different cams, offering various degrees of eccentric design. It allows for the throttle to be twisted less to get get the same amount of "input" to the carbs. It's more delicate then, but full throttle can be had in less movement it being turned. This one I got from a member, but haven't used it yet as it's going on the track bike. I think you may have asked about it before, you can see the 3 different cams, the cables attach to them and it goes in the throttle housing, then the throttle tube fits in.

 
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