FCR upgrade?

[cheap_trix]

I am toying with the idea of upgrading to Keihin FCRs.
I have searched the site and the ones mainly used are 41mm but what specific model?
I remember reading on the old forum that you could get them specificaly for the TRX. Are they still available or can a normal pair be modified?
Are 41mm best? I have seen some 39's for sale.
Any help would be apreciated.

[Killerwhale]

I am toying with the idea of upgrading to Keihin FCRs.
I have searched the site and the ones mainly used are 41mm but what specific model?
I remember reading on the old forum that you could get them specificaly for the TRX. Are they still available or can a normal pair be modified?
Are 41mm best? I have seen some 39's for sale.
Any help would be apreciated.

39´s seems to be enough....i got the 41´s because i know i will do bigger mods to motor later....
http://www.keihin.de has the TRX set, they also make a TPS mount themselves as keihin US doesn´t make them any longer....if you don´t want to go with the TPS mod.

You CAN buy all the parts for pairing up two FCRs, but it´s really easier to buy the TRX set....in my world!

well, what i came to think of now....

You won´t regret it!

[Wombat]

Cheap,

the part no. for Dual Kit FCR 41s for the TRX is 016-671
That's off the Sudco website. But I'm sure you could order them from someone here such as Show 'n' Go in Adelaide.

I'm thinking of going down this route too, 'cos my CVs are 52,000kms old and are really starting to suck performance and economy wise. Plus I had FCR41s on the Guzzi, so I know what they're like.

Bob

[WoTi]

What's the difference between the TDM FCR kit versus the TRX one?
Is the TPS a must, or could it be ignored?

In the Keihin.de site the FCR39 for TDMset was around 820 €.. I have thought that the KEIHIN's are much more expensive than the MIKUNI TDMR40 set..

[phuk72]

FCR41 is the recommended fitment by Keihin for the TRX (although I know that FCR39 does work and can be made to fit) and is the only one to come specifically with TPS. You can fit FCR41 from a Duke 900ss without TPS - all you need is new intake mounts.

Do not buy a bank of 4 to split or 2 singles, it will cost you a bloody fortune!

Not sure about Mikuni TDMR40 having TPS or not or how good they are.

I have been told that FCR41 is the way to go and that they are way better than TDMR40 but the person who told me is full of shit!

You do not need TPS but if not having it necessitates a fairly simple CDI modification.

[trixynut]

FCR 41's are the way to go. Pretty sure that they are all the same, so any off any bike will fit. The only diference is the intake mounting spigots between the carbs and the engine, as Phuk said, which need to be specific for the TRX. These are just aluminium cylinders that just screw in, so can be changed easy if the carbs are not off a TRX previously.

TRX and TDM specific FCR's have the TPS mount on them, but it's better to get ones without and do the CDI wiring mod we figured out on the old forum (I've got a photo for when you need it) to set the ignition at full advance and bypass the TPS. You'll need to get different throttle cables.

My motor is standard inside, but with FCR 41's with foam pod Ramair filters, and a larger bore Renegade full system, power went from 78bhp standard up to 90bhp: yum yum!!

Look at http://www.allensperformance.co.uk for some more general info.

Dave.

[phuk72]

it's better to get ones without and do the CDI wiring mod we figured out on the old forum (I've got a photo for when you need it) to set the ignition at full advance and bypass the TPS.

I have to say I ain't convinced but I'll let you know - the dyno beckons!

[trixynut]

OK, so I don't know of any one who's done back to back dyno runs with FCR's with the TPS connected and then without, so Phuk you can prove a definitive answer on that one.

The point I was making was that if you want the TPS connected, you have to get FCR's that have a connection, i.e. ones that are specific for the TRX or TDM so they are rarer and they probably cost more.

If you don't want the TPS connection, you can look at FCR's off any bike (Guzzi, Ducati, any big twin) so there's more chance of finding some, and then just get the spigots specific to the TRX inlets to plumb them in.

Obviously, if you're loaded and are buying new, this is all irrelevant!

[Max]

I think (over here at least) a lot of people went with the 39mm jobs simply because of the old school thought that smaller bore means higher velocity and better low to mid range performance. Not only that, but pre-acceleration pump carbs required a wrist limiter under hard acceleration to avoid the dreaded baaaaaaaaaaaaahhhhhBANG when opened quickly.

I expected a bit of this myself when I got mine but I find none of that with my 41mm setup and the damned things have outperformed the stock carbs through the entire range while adding a big punch and a lot of noise...

Everyone I've met that had the 39s wished they bought the 41s...

[HansJ]

OK, so I don't know of any one who's done back to back dyno runs with FCR's with the TPS connected and then without, so Phuk you can prove a definitive answer on that one.

...

I did exactly that this summer. I haven't got any prints from the DynoRun, as the tuner had no ink in his printer, and haven't had the time to go and get them...
From memory, disconnecting the TPS wires (we didn't bother wiring according to the diagram, but it should be the same effect), made some 2-3 extra BHP on less than full throttle. I suspect full throttle always retards the ignition fully, so this would be logical. The measuring was very simple, just marked the throttle handle/handle bar with some markings, 1/3, 1/2 and 3/4 throttle. The different runs were however done immediately after one another. Still, there could be a bit of uncertainity in the measurements as we could not guarantee having exactly the same throttle opening. If You have the time Phuk, then measure the resistance from the TPS sensor, that should give a far more accurate reading.

I have the Mikuni TDMRs, have also "heard" that Keihin is "da shit", but I don't know about that. One advantage for roadgoing bikes, is that the Mikunis have choke for cold starting. Otherwise I suspect the best benefit is the flatslide system itself, the difference between 1 mm larger/smaller intake would not really be measureable on even tuned bikes, but that's merely speculation. I know for sure the difference between a lubed/non-lubed chain, it's worth more than the TPS mod...

[phuk72]

2-3 bhp on less than full throttle makes perfect sense and sounds about right.

I have to say I'm more interested in any difference when cracking the throttle fully open lower down the rev range. I suspect not but will know soon enough.

I'll keep you posted.

[HansJ]

If I crack it open, it just coughs, clears the throat, and then starts pulling... With CVs one can do that, but not with FCRs. On the other hand, gaining 2-3 BHP on 1/2 throttle over a CV bike with fully open (but only 1/2 open in practice due to the nature of CVs) makes it worth swapping in my opinion.

[Max]

I should mention for those that may not remember... While my FCRs have the TPS mounting hardware, I have no TPS with the OVER ignitor...

[Max]

The main thing I don't like about CV carbs is it's almost a form of traction control... In effect, separating your wrist from the ground. Sure the MotoGP bikes need this to keep the humans onboard and within Earth's orbit but growing up on racing bikes, I like to get exactly what I put into it.

I ran CR (Keihin) carbs on a SRX600 single (TZ frame) once that required a lot of care on throttle opening. If you weren't careful, it would fall flat on its face (no pump) but I still like that more than wondering if the CV slides really are fully open.

IMHO the TRX isn't nearly as sensitive to any of this as the multis or singles are. Haven't had any problems with cold starts either (three whacks of the throttle are enough to get it popping).

From what I've heard, the Mikunis lack the same build quality unless you get their big dollar racing items. But that's just what I've heard, never tried them myself.

[burty]

I want a set.

Now where can I get me a set for little money?

Phuk, didn't you use something off a Jetski snowmobile or sommat?