makeshift FCR carb builds

[Racer-unk]

Has anyone successfully changed or made new connecting tubes between the carbs......to widen or make them narrower to fit a TRX850?
My take on it is that the downdraft FCR carbs are all the same bar the jetting and are only diffrent in the way they spaced.
Please advise before I waste money......

[trixynut]

Agreed.
The standard Keihin FCR carbs are just that, standard. Then come in banks of 1,2,3 or 4 depending on the cylinders.
The only differences are how to connect them to the specific bike i.e. spacing of the carbs and the spigots to attach them to the cylinder(s) inlet.
Cant help with measurements to fit the TRX though. Really need a pair to take apart and measure I suppose.
Allens Performance do the specific spigots to attach the carbs to the inlets

[cobbadiggabuddyblooo]

Some people have but you need to also look at throttle cable attachment and position plus if you want the advantages that come along with a tps.
The length of the inlet spigots are your next major hurdle because of the ACC pump will foul on the oil filler pipe so it needs to be no less than 26mm once screwed into the carby body ( full length unscrewed from carb body is 35mm )
This is the problem when using Ducati FCR’s which share the same 98mm pitch between inlet centres.
Plus the throttle cable pulls from the rear and different pilots but as a blessing they run the same needles.
Pilots, mains and needles will more than likely all need to changed to a 48 pilot, OCEMP needle, and 150 mains. 200 air jet. Air screw 1.5 turns out, fuel 1 turn out to get you back to default std TRX fcr settings. Some fcr’s Run a pilot air jet and not a screw so be mindful there too.
All downdraught FCR’s have a 2.0 needle / seat on the float.

So add it up for your correct jets, needles, spigots, throttle cable mount PLUS cables ( std Trx cables won’t work) more than likely no TPS which is such an advantage with the fcr’s and corner exit response. Those alone can equate to 2-300 $$$

Plus look at if they have airbox mount adaptors or bellmouths.
Bellmouths are the way to go.
You could fit pod filters to you airbox mounts but your loosing on flow. Even the shape of the bellmouths itself can give you gains.

Most block of 4 FCR’s use red 35mm bellmouths which are great if your rpm is between 8-12,000
But you want the blue 50mm bellmouths which are tuned lower between 6-9000 rpm.( another $100 and that’s before air filter choice)
Good chance you’ll need a gasket kit too.
I was selling refurb fcr kits a while back for about $200 from memory that had new needles, clips, tubes, float needle and seat, gaskets and o rings and that was dirt cheap due to a bulk purchase of all the parts to keep costs to a minimum for the forum members.


So i’ll let you do the maths and factor in the time, effort and stress.
It can turn out to be a big shopping list if you want the most from your new investment.
Not quite as simple fix as a axial mounted radial caliper.

[dicky]

It's like asking if an FCR taken from a Honda XR650 could fit onto a KTM 640
Sure, it could, but you would have to source a lot of bits.
Inlet spiggot
Airbox adaptor vs bellmouth
Throttle cable adaptor
Throttle cables
Jetting

Ask me, I did this, it was not worth it.
Trying to adapt a multi-carb setup would be, in my egotistically inflated opinion, not worth it.

[Racer-unk]

I have dropped pics on Yamaha TRX850 facebook pics.

[Racer-unk]

i can have it for equivalent of 500 A$
Cables are cheap to make locally, even if I have to do it twice.
Blue bell-mouths...check
Jets I can get locally....check
Needles...well lets pray....
Engineering should be a minor issue.....if i cant do it myself

[PrfctChaos]

What bike are the FCR's coming off? I didn't see that mentioned.

[cobbadiggabuddyblooo]

Saw them on his Facebook post and 39mm FCR’s off a Kawasaki and most boxes are ticked with throttle cable attachment position, blue bellmouths and intake spigot length.
Won’t have a TPS will need cables, pilots, mains and needles to suit TRX jetting plus correct spacing to 98mm pitch between centres.