FCR jetting

[Riceburner]

As you know I'm going the FCR41 conversion on my car, Just wondering if anyone knows of it being done before and what sort of jetting will be a good starting point? I've done heaps of searching with not much luck, seems likes it's done a little in japan.

[dat2kman]

Ina Japano Mr Garetho!!

Pleasea exeplaina FCR41 ??

 

I thought, hhmmm, a new carburettor type here!

[Riceburner]

Sorry I should've put in the full name 

Keihin FCR41's.....They are flat slide carbs, no throttle shaft or butterfly so the slide is connected to a common shaft in the top of the carb. Very common on race bikes.

 

Currently I have 220 or 230 mains in the 42mm Keihin VP on the car, but these are vacuum slide operated and also have a butterfly similar to su's. The FCR's have an accelerator pump on each set.

[peter mc]

you need to try them mate and find a starting point , then ask a race bike shop for help with jetting

[Riceburner]

Hmmmmm yeah thats kinda what I thought.

 

Might be a silly question but would a bike tuning shop only have a single wheel dyno? Lol.

[peter mc]

heheh yes mate but you just need there jets and tune it on a normal dyno

[roastbeef]

I have these companies bookmarked for the Honda S800. They appear to have done a few FCR conversions on cars.

http://www.v-performance.com/products/air_fuel.html

http://www.phildentonengineering.com/product.asp?pid=506

 

Also try sending a message to Alan (HS30-H).

I remember enquiring about this setup on another forum a few years ago and he had some information, or could possibly lead you in the right direction.

 

 

[dat2kman]

Aha, flat slides, just a thought, the volume of the air pump (cylinder) allowing for valve overlap and cam duration, will compress a particular amount of air for each firing stroke, jetting would pretty much be based on the relationship of air to fuel ( fancy name, stoichiometric ratio) so if a known amount of fuel needs in perfect terms about 14 parts of air, the jetting rhe bike guys use, based on their cylinder volumes, cpuldossibly be calculated out to your cylinder volume.

 

Maybe weld a bung fitting on the exhaust at gearbox for a wide band lamba sensor, to monitor air/fuel?

 

Next oddity, how do these flat slides go, say, in a situation of almost wide open throttle, you lift off gas pedal, downchange to lower gear, hit brake pedal, these action cause a fair amount of vacuum, ,, will the vacuum friction affect the flat slide mechanism?

Maybe try a decent household vacuum cleaner on the engine side of one of them, open it, start vacuum, and release the open slide, stiffer return springs??

 

I had a Kawasaki Z1R mk 2 many moons ago, back when Suzuki made a hairy tbing called Katana, it had the flat slides, i always wondered about how big these got for car use. Honda S600 and S800 sports cars ran them, light car small engine, but i think their carbs were not quite like the normal bike carbs. Interesting!!!

 

On a bike, far less compression vacuum on deceleration, the slides will close.

 

I have often looked at rhe lens mechanism of old SLR film type cameta's, at the iris leaves, as you twist the aperture opening ring, in place of a butterfly in a normal carb or TB, again vacuum could be an issue.

[RB30X]

Jason in all seriousness, are you on speed?

[dat2kman]

Jason in all seriousness, are you on speed?

No no no, just sometimes i remember donkeys ages ago i like think, uuummm, motorbike carbs on a car???

Then i think, whats an alternative to a butterfly, a camera iris aperture thingy, i'm like thete in  1985 thinking this weird stuff! Never happens.

The a/f thing is good, got it on the Z and the 120y, play with jets on the Y, go for hard drive, then play again, ypu either go the right eay, or go worse, works good!

In the Z i was playing with temp sensors using different value potentiometets and resistors, do a temp solder up, play, go for a run up long driveway, check lambda read out, lot of fiddling, but got it pretty right, i think!

The Y runs fat around 12;1, better that eay, wont lean it out.

I did lean out Z burnt pistons etc, thats how discovered the intake runners are " not right" from factory on inject manifolds.

 

What part of my ramblings suggests tje ingestion of goey??

[peter mc]

mmmmm you funny bugger you dont need wipper your mind is going so fast .....

[d3c0y]

With a 2.8L / 6 you are only getting 466cc per cylinder. 1000cc V-Twins have more capacity per cylinder and probably running more compression so I don't know if the vacuum thing would be an issue?

 

Just googled - Ducati 900ss, KTM 950 Adventure

 

Anyway this page also lists a basic tuning guide for FCRs - you did search the Internets already though right?

http://www.ducatitech.com/2v/fcr_faq.html

[d3c0y]

mmmmm you funny bugger you dont need wipper your mind is going so fast .....

 

Lol faster than his fingers can press the letters by the looks! 

[dat2kman]

With a 2.8L / 6 you are only getting 466cc per cylinder. 1000cc V-Twins have more capacity per cylinder and probably running more compression so I don't know if the vacuum thing would be an issue?

 

Just googled - Ducati 900ss, KTM 950 Adventure

 

Anyway this page also lists a basic tuning guide for FCRs - you did search the Internets already yet though right?

http://www.ducatitech.com/2v/fcr_faq.html

Yep, jake, im not up with the big bore twins, they maybe run some sort of bypass tubing when the throttle snaos off on decceleration, i was going back to old days i can remember my old bikes a Kwaka Z650 then a 900 then the Z1R, a mate had a flexi frame Kwake KH 750 two stroke, horrid thing, missile quick, he put it in a Rickman frame tjat fixed it, we'd go down to Rosebud of a Fid nite, for a run, or down Ocean road to Wye river pub, sleep on lawn out front, those things had the flat slides, but capacity of the four pots were small, plus overall wright wouldnt have been a vacuum isdue on compressipn.

Yeh yeah, i know sometimes my fig bat fingers hit the  wrong keys on the keyboard, but yes i type to quock, mostly on Ipad all time, convienent to pick it up, bang away, as well as type on the ipad, missus whinges a bit, reckons i shouldnt do two things at once, lets see who read all that!!

[Riceburner]

Thanks for the info so far guys there is some helpful bits there  Tuning isn't a problem as I have an air fuel meter but I was hoping to get a really good starting point by finding jetting specifically for the 'L' series motor.

 

The slides each have 4 rollers on them to make operation silky smooth and as they are fixed to the shaft a throttle return spring will snap them closed.

 

The old carbs off a cbr1100xx had 150-160 mains from the factory, I've gone through nine jet changes and various other mods to end up with approx 220 mains now so it can be fairly time consuming. Amazingly they did run straight away at that size with no coughing or splutters, just didn't have much grunt. I hope the Fcr's are as easy!

 

With the Fcr's having acc pumps i thought it will be harder to tune as the extra squirt of fuel when opening the throttle may hide the true tune

 

I'll shoot Alan a pm, hopefully he has some specific jetting info or knows someone who does.

 

 

 

 

[d3c0y]

I think that the base settings on the site i posted would be a good starting point. The ducati 900SS is 450cc per cylinder and if you have a 2.8L you have 467cc per cylinder. Checkout the specs of the Ducati 900 Super Sport below. It's making 40hp per cylinder and just under 100hp per litre. So if you have an L Series doing those kind of figures you will be pushing 240hp at the crank which is about right for a trick carb setup 2.8L with some head work, it's even a 2 valve OHC!:

 

Engine

904 cc SOHC 2-valve Desmo L-Twin

 

Bore / Stroke

92 × 68 mm (3.6 × 2.7 in)

 

Compression ratio

9.2:1

 

Power

80 hp @ 7,500 rpm

 

Torque

57 ft·lbf (77 N·m) @ 6,500 rpm

 

Base Jetting for 41 FCRs on Ducati 900SS:

 

Fuel screw

mixture screw

3/4 turn

 

Slow Air Screw

1-1/2 turns

 

Float height

9mm

 

Main Jet

155

 

Main Air Jet

200

 

Slow Jet

60

 

Needle

EMT

 

Needle Clip

3rd from top

 

That article says that it's a little rich from the factory so i think this would have you gunning close to a decent mixture on the L.

[Riceburner]

Seems small compared to the current setup and I would hope the FCR's will flow better, hopefully a good start point though 

 

Would a weber or mikuni setup with 40-41mm chokes be more comparable, maybe jetting sizes from this type of setup would be close to the mark? The FCR's should flow better than weber or mikuni as the only restriction at WOT is the needle......

 

It all gets confusing! Lol

[KatoKid]

Hey Gareth.

 

Try http://www.showandgo.com.au/ they are the Keihin distributor for Aus. Cant remember the name of the guy that started the business but he is a legend in the bike world.

 

David

[Riceburner]

Thanks David, with the amount of emails I'm sending I'll have to get a few good ideas. Lol

[Riceburner]

I think that the base settings on the site i posted would be a good starting point. The ducati 900SS is 450cc per cylinder and if you have a 2.8L you have 467cc per cylinder. Checkout the specs of the Ducati 900 Super Sport below. It's making 40hp per cylinder and just under 100hp per litre. So if you have an L Series doing those kind of figures you will be pushing 240hp at the crank which is about right for a trick carb setup 2.8L with some head work, it's even a 2 valve OHC!:

 

Engine

904 cc SOHC 2-valve Desmo L-Twin

 

Bore / Stroke

92 × 68 mm (3.6 × 2.7 in)

 

Compression ratio

9.2:1

 

Power

80 hp @ 7,500 rpm

 

Torque

57 ft·lbf (77 N·m) @ 6,500 rpm

 

Base Jetting for 41 FCRs on Ducati 900SS:

 

Fuel screw

mixture screw

3/4 turn

 

Slow Air Screw

1-1/2 turns

 

Float height

9mm

 

Main Jet

155

 

Main Air Jet

200

 

Slow Jet

60

 

Needle

EMT

 

Needle Clip

3rd from top

 

That article says that it's a little rich from the factory so i think this would have you gunning close to a decent mixture on the L.

 

Decoy, your post got me to do a heap more searching and cross refrencing of my current jet sizing vs. similar jet sizing per cubic capacity I've reviewed the sizings from the ducatti... main air jet 200, float height, needle clip 3# are all very close to current set up. They don't mention pilot air cause they use an aftermarket adjustable screw (available at $20ea.), I have 100# pilot air in both the CV's and FCR41's so will stick with those too.

 

Because the pilot/slow jet is so big at 60 they only have the mix screw at 3/4 turn, so this with the accel pump could be masking the true tune which is why they use 155mains. I found a few other FCR41 setups with similar cubic capacity to my worked L29 running on average 185mains, 45 or 48 pilots, 200 main air, 100 pilot air, 2 turns on mix screw and the needle on the third clip.

 

This will probably be a good starting point that will run fairly well but won't have huge top end I suspect. Time will tell, stay tuned.

 

   

[dat2kman]

The correlation to Webets is uncanny!

 

[Riceburner]

The correlation to Webets is uncanny!

 

 

Really Jason, What sort of setting would you expect when running 41mm chokes?