FCR's... how good are they really?

[Overlord Neil]

This is a total amateur question, there is constant reference to FCR's for the TRX, alot of guys here seem to be racers where i can understand the pursuit for outright performance and any gain is worth the investment (sort of but you know what I mean) for a road rider how much difference is there really? Do they significantly increase fuel consumption or are they just better at metering the fuel that is used?

I use my bike daily to commute, it works great as it is but I'm a habitual tinkerer so any 'improvement' always need to be considered. I think my bike is running the standard carbs, though it has been dynojetted and has a K&N filter in the original airbox, I'm also running 2 into 2 straight pipes on open Remus Carbon Cans. I'm averaging 40 MPG, though I am fairly heavy handed and there are a couple of arrow straight roads that require high revs in top gear...

[cobbadiggabuddyblooo]

Tune your suspension and upgrade brakes and you'll benifit more for the money spent.
Buy yourself a spare keyster carb kit to rebuild the carbs and TCIP4 ignition and you'll still have change for what you'll pay for FCR's.
You can tinker with the timing, tyre pressures and suspension then.
personally I think the TDMR 40 is a much better choice as you'll find a little more torque and more velocity down low so more useable midrange.

[Overlord Neil]

Hi Cobba,

The bike came with blue spots, after market rear shock and reworked forks though I'm looking at putting some conventional R6 forks. Eventually, I'm hoping to have a.n.other bike as my regular runner and then that will allow me to tinker at will with the TRX.

[dandywarhol]

Have asearch for my post on Litetek carb overhaul kits. The are made from Viton and cope well with the shitty ethanol fuel we have to put up with today
http://www.litetek.co/index.html

I've never used FCRs but I remember mincehead's bike reeking of petrol from the K + N filters throwing fuel back out at low revs

[drix]

I run FCR41's with a 2-1 exhaust, ignitech ignition & Dyna coils... I do a mix of commuting into central London, motorway miles & weekend rides in the country. Usually spirited riding, I get circa 220km to reserve. I find them very civilised considering, cold starts even in winter are never an issue (47000km engine, always fresh plugs/oils/filter) & the roar/added power is pure pleasure... I don't see any drawbacks except for their cost.. But then again I'll never sell them on & I see them as a personal treat/investment

I have another standard but cafe'd TRX which is nice as well and a good reminder of how a more of less stock TRX & engine behaves... Both bikes end up feeling very different but both are just as lovely!

Tricky decision here but at the end of the day, which ever way you go, I don't think it'll be a wrong decision..

[Trixed]

I have a very early Japan model and an Australian model.

Before I changed I used to get 260 to reserve, now it is 310 to 317 to reserve. Extremely happy overall. I actually had a concern about the fuel economy but that has actually improved and is better that my stock carbie bike which is in very good nick. The bonus is also the induction music and whistle.

I also have Nojima twin exhaust, Ignitech ignition and correct jetting by Cobba which really helps the FCRs.

All FCRs are expensive but its a one time investment for life, you wont regret it. In fact in my case it is paying itself off with fuel savings.

[alextrx850]

Well,said comments to Drix and Trixed.
The throttle pump in the FCRs and the TDM 40s will give an instant power push on aggressive acceleration.
Mind that if you've got more carburettor volume, you will need more elsewhere as well, so unless you are going to spend to upgrade the head and the exhaust flow, the money will be better spent elsewhere as cobba suggests.
I've just rebuilt my spare motor with a well flowed head and seated valves by an engineer...that with my FCRs and the projection components over bore two into one exhaust ,..makes for a surprisingly better performance.
In short, the cost of better carburettors should be the start of the bigger picture.
Otherwise the origional Mikunis are ok as well.

[cobbadiggabuddyblooo]

Choice of exhaust can be a source of the excessive fuel problem mince was experiencing.
If the exhaust pulse is tuned more for the upper rpm range , with the 41mm FCR bore you lack velocity and the exhaust pulse can actually force some fuel back up the inlet tracts.
The reason I suggested the TDMR 40 mm.
Hey homogenise the fuel a little better too down low with the style of emulsion tube they use and ultimately are a much better all round carburettor designed for a motor and not specifically for race use like the FCR's.

[Overlord Neil]

Great responses, thank you all for excellent information. Ultimately it comes down to want....? I'm looking to invest a fair bit of time an effort on the old Trixxie over the coming months, to graft an Aprilia into it so i might have to put the performance mods on a back burner.

The fuel saving is a very interesting point, given that after the move I'll be doing 90 miles a day, so thats... 90x5=450 miles a week 450x48= 21600 miles a year @ 40 MPG, 21600/40= 540 Gallons of fuel @ 1.00 litre: 540x4.5= 2430 litres = £2430 fuel costs. If Trixxed is getting nearly 20% more mileage from his FCR's; 40x1.2=48, 21600/48= 450 Gallons of fuel @1.00 litre: 450x4.5= 2025 litres = £2025 fuel costs, so I've saved £405 already... If the cost of fuel goes back up to £1.5 litre; (2430x1.5= £3645) - (2025x1.5= £3037.5) = £607.5

I'll order some now...

[dicky]

CV carbs are almost always more economical that flat slides. They are designed to be. It's why they use them as original equipment on most bikes and cars before injection became the norm. They are also very forgiving, you don't have to adjust them if the weather changes
Flat slides have instant throttle response which is great for track work but means nothing if they are not correctly set up and jetted. You can stall a bike with flat slides just by cracking open the throttle fully at low revs.
Standard TRX jetting on the BDST38's is rich, at least here in Oz, so checking that what you've got is actually set up correctly might be a good starting point before spending serious cash on flat slides to 'make it better'.

[dandywarhol]

CV carbs are almost always more economical that flat slides. They are designed to be. It's why they use them as original equipment on most bikes and cars before injection became the norm. They are also very forgiving, you don't have to adjust them if the weather changes
Flat slides have instant throttle response which is great for track work but means nothing if they are not correctly set up and jetted. You can stall a bike with flat slides just by cracking open the throttle fully at low revs.
Standard TRX jetting on the BDST38's is rich, at least here in Oz, so checking that what you've got is actually set up correctly might be a good starting point before spending serious cash on flat slides to 'make it better'.

how rich are stock carbs Dicky and do you have recommendations for jet sizes/needle positions? I once tried Factory Pro needles to match the jets and had a real hard time setting them up - they run richer than stock - I ended back to Yamaha needles

[cobbadiggabuddyblooo]

138.5 and 140 are the common jetting down under. UK is similar air density as here in Australia and 1 reason the keyster carby kit is popular here as it gives you a choice of 142 and 140 mains.
Even the FCR set up is rich with its 150 mains on a TRX unless you have a larger bore system like an Over or Nojima that are specifically tuned for 6000+ RPM.
I suggested to Alex to go down to a 145 with his projection components system and he found improvements.
Now that will prob change after a little head work back up to a 150 because it will graciously flow a little more.