Keihin FCRs Vs Mikuni CV carbs

[koko64]

A year ago I was riding my 900 Monster on the road to Damascus when I had an epiphany. I had a vision and nearly fell off my bike. The vision was not what I expected because He didn't appear, it was bloody Chris Kelly (more akin to El Diablo)!

Chris said, "Why brother are you wasting your time with jet kits, dyno time and generally make the beast with two backsing around with the stock Mikuni carbs when salvation is at hand? You have modified your motor, you are pissed off with carb freezing and frustrated that you cannot get the stock carbs to meet your requirements. Who the hell do you think you are, Doug Lofgren?"

"I would not presume to compare myself to brother Lofgren", I answered, "I just thought I could...". "Silence", he said, "Stock carbs are an abomination upon modified motors, require new needle jets every 5000 miles and give people the shits in cold weather. Buy Keihin FCRs. Oh, and don't be a pussy, get the 41s for a 900 motor", he added.

And then he was gone.

Pondering this I realised I had spent $300-00 on jet kits, $70-00 on needle jets, $200-00 on dyno time and countless hours tuning, researching and test riding. The FCRs are expensive, but they are half the price in the States compared to Oz. If you have a stock bike, don't ride in the cold and don't ask anything too much of your motor, then get a jet kit and accept the limitations, but if you ride all year round, have modified your motor or ride hard there is an answer.

[Travman]

So have you ordered them?

[koko64]

They've been on for a year. A recent thread on CV carbs prompted me to start this thread.
I was wondering when I'd get a bite.

[Travman]

and... are they everything you've been hoping for?  Is there a noticeable difference when you open the throttle? 

[monstermick58]

C'mon KoKo,

Tell us, Tell us, Tell us, Tell us, Tell us, Tell us, Tell us, Tell us, Tell us, Tell us, Tell us, Tell us, Tell us, Tell us, Tell us, Tell us, Tell us, Tell us, Tell us, Tell us, Tell us, Tell us, Tell us, Tell us, Tell us, Tell us, Tell us, Tell us, Tell us, Tell us, Tell us, Tell us,









                                      Mmick

[koko64]

They are absolutely bloody awesome.

Power wheelies from corner to corner through a series of S bends on your favorite mountain road. The wheel comes up on each corner exit and transition through the esses. You know, kinda "ski boating" along.

The throttle response makes the bike feel like it has gained 10hp when peak hp is only a few (2-3) more. It is the acceleration that is drastically different. In short Chris is not overstating his claims about them. They are much easier to tune than the CVs with very little compromise. My friend says his bike (98 M900S) is much more responsive than his former 2000 M900S. Both had the same intake and exhaust mods, open A/B and pipes, one has a tuned FIM ECU, one FCRs. The connection between throttle and rear tyre is immediate and direct.

Another advantage is the tuning logic is linear. This is no surprise as the main jet directly feeds the needle jet and sits beneath it low in the float bowl. It has a feeding effect right through the rev range and can effect as low as 1/4 throttle. The needle moves with the slide as you turn the throttle. There is a circuit to tune each increment of throttle position. The 'fuel draw' is excellent.

I have ridden in zero deg C with no carb freezing. My bike was previously unridable in those conditions. Melbourne has developed incredible humidity to go with it's changable weather.

My fuel economy has improved. I am using less throttle for the same forward motivation. The accelerator pump lets you run an economical midrange cruise setting as it takes care of sudden demands for acceleration.

Looking at my invoice I have actually had the carbs on for twelve months! The year went quick. I can't believe it, so I will edit my original post. It just struck me how long I persisted with modifying the stock carbs on this current bike although I learned a shipload. My wife bought me the carbs when she took pity on me after watching my tuning efforts with the stock carbs over two years. The stock carbs were a weak link in my engine mods and didn't let the porting fulfill it's potential (my opinion). They completed the package and update the intake system short of fitting fuel injection.

I had a Superlight with a modded engine and 39 FCRs but it came with them so I had no back to back comparison. I was spoiled with that bike and so dissappointed with the stock carbs this time around. On this bike I had a back to back comparison and feel I wasted valuable time. I reckon that certain riders should put them on as soon as they buy the bike. For many I feel the open A/B, tuned FCRs and slip on pipes will be the only mod they will ever need for a street bike (well maybe dialed cams and better coils too).

I will soon be dyno testing if they work best with pods or air box with long or short rubber velocity stacks.

There is only one downside besides price; no coke/enrichement system. You squirt the accelerator pump to prime it in cold weather. But you learn a system that works.

Understand that I do not distribute these carbs or sell them. I have no business connection with Chris except for being another customer. I mention Chris in my analogy only in good humour. I don't actually know him except a couple of emails. I usually deal with the charming Candice.

I think that there is more money to be made tuning the schizophrenic stock carbs for an ok but not brilliant result.

[Nomad]

Glad to hear this!  One of my winter mods was putting on the Keihin FCR's.  Bike is still in too many pieces to turn on yet, and awaiting more parts before it is even close to ready, but the new carbs are on!  One thing that made installing them nice was reducing the hoses to the carbs to a  single fuel line, vs I think 5 different hoses on the stock set!

[koko64]

Yeah, I forgot about that.

Delete ugly vacuum chambers. Less two spring covered vacuum tubes and filters, minus one overflow hose and minus one hose to the left vacuum chamber.

Choke cable, lever and throttle return cable gone.

Clean.

[ducpainter]

Did you get split singles or the banked set?

Pods or stock airbox?

[greenmonster]

Yup, easy to get religious over FCR`s, they are baaad.

But you forgot one thing, koko, the lovely NOISE !!!
At least w pods, the chirping like a bird nest at small openings, a promise what is at your disposal w a simple flick of the wrist.
And, the ROAR of a horny fullgrown bull at WOT!

[Düb Lüv]

But you forgot one thing, koko, the lovely NOISE !!!
At least w pods, the chirping like bird nest at small openings, like a promise what is at your disposal w a simple flick of the wrist.
And, the ROAR of a horny fullgrown bull at WOT!

+1 

[Drunken Monkey]

Great, now you've reminded me how awesome they were on my 900ss and I'm going to have to go out and get one (yes ONE) for my Duke.

Damn you for forcing me to spend money!

[koko64]

Did you get split singles or the banked set?

Pods or stock airbox?

I got the banked set. I investigated getting split singles but I did not want to relocate the frame cross member in the way. You could fabricate medium length inlet manifolds and work around it, but in the end the 4-5 hp increase at the top end may take a similar amount away from the bottom end from some dyno charts I've seen. It appears the greater the capacity/compression, the less loss down low with the short manifolds. I consulted a few people in the States who have used short manifolds and decided to stay with the banked set on my stock bore bike. On a street bike I was happy to keep the torque peak lower, although I am still open to experimenting in the future!

I am running an open air box with K&N filter. I have trimmed the rubber velocity stacks and radiused them so they are flush with the air box and sit back about 20mm further from the filter face. I recently relocated the breather hose to under the left ignitor (over the battery) to more allow room for the throttle cable.

I will soon be testing pods Vs open A/B, long Vs short velocity stacks and breather hose on Vs breather hose off on a dyno.

[koko64]

Great, now you've reminded me how awesome they were on my 900ss and I'm going to have to go out and get one (yes ONE) for my Duke.

Damn you for forcing me to spend money!

What stock carb does it have?

[koko64]

dp

I think that you should borrow a set from someone and try them. Then you can decide if they are worth the money.

When you are just taking it easy, say cruising through some mountains with a pillion, you can feel the clean, crisp and smooth carburation. Like a 60's/70's small block V8, fitting a modern carburetor package updates the performance of a great real world motor.