Keihin FCR 39/41

[s3dxm]

Hi,
I'm looking at installing a set of FCR's on my 1314 FJ.

Does anyone have any recommendations for jet sizes etc...

Just pie in the sky at the moment - but may become a reality...

[Pat Conlon]

Paging Frank, (aka:Flynt) please pick up the courtesy phone....

[Flynt]

Hi,
I'm looking at installing a set of FCR's on my 1314 FJ.

Does anyone have any recommendations for jet sizes etc...

Just pie in the sky at the moment - but may become a reality...

I have dyno tuned FCR39's on a 1349cc with big valves and cams...  happy to share my specs when you're ready. 

My experience in a nutshell...  The stock XJ jetting that came with my set of carbs ran on my bike, but not very well.  Frank from the East, also a FCR39 user, gave me his specs and I ran that with good results for a while.  Dyno made lots of changes, especially in high RPM fuel flow...  not sure which setup will work best for you, but we have a couple to offer for you to try.

Frank

[Flynt]

Hi,
I'm looking at installing a set of FCR's on my 1314 FJ.

Does anyone have any recommendations for jet sizes etc...

Just pie in the sky at the moment - but may become a reality...

I have dyno tuned FCR39's on a 1349cc with big valves and cams...  happy to share my specs when you're ready.  

My experience in a nutshell...  The stock XJ jetting that came with my set of carbs ran on my bike, but not very well.  Frank from the East, also a FCR39/1350cc user, gave me his specs and I ran that with good results for a while.  Dyno made lots of changes, especially in high RPM fuel flow...  not sure which setup will work best for you, but we have a couple to offer for you to try.

Frank

Come to think of it...  Travis (TLegg) has another Keihen combo to share I think...  You're going to be fine, but I would consider a dyno tune to get it perfect anyway.

Frank

[fj1289]

Be aware tuning FCRs are a bit more involved than most carbs.  This is a good thing - it is because of their run ability and how well they "track" the fuel curve at all RPM ranges.  

Most carbs you primarily tune via the fuel circuits.  The FCRs are also very tunable for the air circuits too.  This gives you the ability to not just make a circuit (like the main circuit) richer or leaner, but can tweak it to exactly what the motor wants - it may want the "bottom" of the main circuit richer comparatively than the "top" of the circuit - - or maybe the opposite - maybe it needs to get richer as you get through the main circuit.  Balancing the air jets vs the fuel jets lets you tailor that "curve" for a particular circuit.  

FCRs can be a real weapon in the hands of a good tuner.  

[T Legg]

Come to think of it...  Travis (TLegg) has another Keihen combo to share I think...  You're going to be fine, but I would consider a dyno tune to get it perfect anyway.

Frank

      Actually I'm running Mikuni RS-38 flatslides on an a stock bore FJ1100.They are cheaper (around $900.00 US ) and simple to tune . They do not have roller slides and they have a very stiff throttle spring but I love them. I've never tried the Keihen flat slides, I might like them even more.

[FJ1200W]

Come to think of it...  Travis (TLegg) has another Keihen combo to share I think...  You're going to be fine, but I would consider a dyno tune to get it perfect anyway.

Frank

      Actually I'm running Mikuni RS-38 flatslides on an a stock bore FJ1100.They are cheaper (around $900.00 US ) and simple to tune . They do not have roller slides and they have a very stiff throttle spring but I love them. I've never tried the Keihen flat slides, I might like them even more.

I have a set that I need to use, but they are set up for methanol.

Could I run E85 with that jetting or would you have any idea on where to start?

1315cc, high compression pistons (I need to do some measuring, they are more than the 10.5:1's) megacycle cams, etc.

Thanks in advance

[Pat Conlon]

Could I run E85 with that jetting or would you have any idea on where to start?

Chris is the guy for this...I would imagine you have to move a higher volume of fuel from your tank to your carbs to compensate for the ~30% lower energy density of E85.

Good news is that you already have a fuel pump.

[T Legg]

I have a set that I need to use, but they are set up for methanol.

Could I run E85 with that jetting or would you have any idea on where to start?

1315cc, high compression pistons (I need to do some measuring, they are more than the 10.5:1's) megacycle cams, etc.

Thanks in advance

I don't know anything about running methanol or E-85 gas.Unless you want to run alcohol I would re-jet them for gas. I use E-10 gas because I don't have a choice.I'm at 5000 ft and I've found the factory recommended settings were pretty close to right. The settings are the same for 1100's as 1200's so I don't think your extra displacement is a major factor but you might need a larger main jet and different jet needle height especially at your lower altitude.
       The factory settings are a 135 main jet , 17.5 pilot jet , 9CHY3 jet needle with the clip set at -2 , and a Y-6 needle jet. Jets r us carries all the parts.
           I'm currently using those settings except the jet needle is at -3 . It's also important to have the accelerator pump set to start about 1/4 throttle and stop by 3/4 throttle. The fuel screw setting is 1/4 turn to 1/2 turn out.

[Pat Conlon]

Trav, I don't know what carb you're referring to but, my stock Mikuni jetting was nowhere near those sizes.
My needles were fixed, pilots 37.5, mains 110 and 155 air bleed.
The USA bikes were jetted lean.
The EU bikes had different Mikuni jetting, they had adjustable needles, 42.5 pilots and 112.5 mains.

I'm not aware of any FJ coming from the factory with 130 main jets.

Dyno jet made an aftermarket jet kit for our FJ's and those jet sizes used different size numbers than the Mikuni sizes. 

What I found when I went to a bigger engine is that you most definitely had to adjust the jetting to compensate for the added volume of air those big pistons were ingesting. It's logical, you are adding 20% more air into your engine, might as well plan on adding 20% more fuel.

[fj1289]

Could I run E85 with that jetting or would you have any idea on where to start?

Chris is the guy for this...I would imagine you have to move a higher volume of fuel from your tank to your carbs to compensate for the ~30% lower energy density of E85.

Good news is that you already have a fuel pump.

Methanol requires even more volume than E85.   I'd assume you'll be good to rejet from the meth setup for E85.   Don't really know how much you'll need to take out - maybe go 10% smaller area on the main jets and drop the needles a notch and see if it will run.  Keep stepping down in 10% increments until you get it to run, then you can start tuning.  

Let me add - I have used E85 and ethanol based fuels in the street bike and race bike - BUT I haven't done it with carbs - just EFI

[T Legg]

Trav, I don't know what carb you're referring to but, my stock Mikuni jetting was nowhere near those sizes.
My needles were fixed, pilots 37.5, mains 110 and 155 air bleed.
The USA bikes were jetted lean.
The EU bikes had different Mikuni jetting, they had adjustable needles, 42.5 pilots and 112.5 mains.

I'm not aware of any FJ coming from the factory with 130 main jets.

Dyno jet made an aftermarket jet kit for our FJ's and those jet sizes used different size numbers than the Mikuni sizes. 

What I found when I went to a bigger engine is that you most definitely had to adjust the jetting to compensate for the added volume of air those big pistons were ingesting. It's logical, you are adding 20% more air into your engine, might as well plan on adding 20% more fuel.

                  The RS-38 flatslides that Steve wants to try on his 1315 cc motor. The factory settings I was referring to are what Mikuni suggests when putting these carbs on an FJ1200. I agree with his larger engine he might need to increase jetting and or raise the needle setting but I think the needle and needle jet would be fine, when using gasoline or E-10 .

[Pat Conlon]

Oh.....Ok, gotcha, thanks Travis, good to know.

On my 1380 with the BS36 Mikuni's I had to raise my needle all the way up to get the a/f ratio where it needed to be.

Cheers

[s3dxm]

Hi,
I'm looking at installing a set of FCR's on my 1314 FJ.

Does anyone have any recommendations for jet sizes etc...

Just pie in the sky at the moment - but may become a reality...

I have dyno tuned FCR39's on a 1349cc with big valves and cams...  happy to share my specs when you're ready. 

My experience in a nutshell...  The stock XJ jetting that came with my set of carbs ran on my bike, but not very well.  Frank from the East, also a FCR39 user, gave me his specs and I ran that with good results for a while.  Dyno made lots of changes, especially in high RPM fuel flow...  not sure which setup will work best for you, but we have a couple to offer for you to try.

Frank

Hi Frank.

When you have the time I'd be most grateful to know the specs you've been running.

There is a local old school bike dyno rolling road near me - so if I could achieve a good baseline setting I'd be a step in the right direction...

[Flynt]

Hi Frank.

When you have the time I'd be most grateful to know the specs you've been running.

There is a local old school bike dyno rolling road near me - so if I could achieve a good baseline setting I'd be a step in the right direction...

East Coast Frank's jetting (No dyno data, bike would not hold a load above 6K RPM):
Main Jets = 148
Slow jets = 55
Slow air mixture screws = 1 & 1/8 out
Air bleed screws =  4 turns out
Float Height = 9mm
Needles = XJR1300 spec

After FactoryPro tune (130WHp, 80.3 ftlb on Eddy Current Dyno):
Main Jets = 152
Slow jets = 55
Slow air mixture screws = 1 & 1/4 out
Air bleed screws =  4 turns out
Float Height = 11mm
Needles = FP spec proprietary

Hope that helps...

Frank