Yamaha TRX850 Enthusiasts Forum

Hi all,
anyone know off hand what the carb spacing is?
ie- the inlet tracts are how far apart OR how far apart are the carbs from each other?
Gotta space the fcrs correctly, they came off a straight 4

cheers,

Would they still be downdraft type carbs to suit the trx or if they are what did they come off if you don't mind me asking

Give Allens a ring:

http://www.allensperformance.co.uk/contact.html

And yes, they do need to be downdraught types.

Hi Cobba

They came off a ZX-9 - ebay in the states.
I await delivery with trepidation!
I will split them and set both pair up for TRX if someone is interested in a set of '39s,

Well they`re definately downdraught versions for the ZX9R so that`s a good starting point.

http://www.sudco.com/CatalogJPG/064.jpg

Click on the images to zoom.

What I need is millimetres.
Like what you UK fellows use but updated to post jesus times.

I can measure my old engine tonight, do you want centre to centre of the inlets or...?

Let us know how you go, I've always been under the impression it would be too hard/expensive to split a bank of four.

be interested on how you go with this project also. do you have a pair of 41's down there somewhere you can copy off???
There's a few of us here with them so if any lengths are needed on things I'm sure someone maybe able to accomidate.

Thanks Mick, centre to centre would be fine!
I will keep all updated on the split

it springs to mind, and i'm taking a stab in the proverbial, that if both 41s and 39s only differ in bore size not body size, could you not use 41 bracketry to set a pair up?
do they share shaft size?
etc etc
cheers
fung

they use the fluid feeds as the spacing brackets tho as you can see in the link mince supplied...
just a matter i spose of sorting the throttle linkage then from one to the other.
????? on the second pair .... theres only one on the side of the bank of 4 by the looks
but you never know what he may have in his bagmaster of tricks

Check out this link with the pic on FCR 41's for TRX
http://www.ebay.com.au/itm/016-735-Yama ... 4cfe293ec2

This may be more of interest, click on it to zoom the image:

http://www.sudco.com/Diagrams323728/expfcr.gif

Spend a little time there and you can ascertain the part numbers you require, and yes it seems all the FCR`s share alloy spacers, link tubes and spindles, varying lengths obviously to suit application. I actually split mine when I first got them, they got an ultrasonic clean before reassembly, setting up and fitting to the bike.
I set the slides with precision ground round pins and they were almost perfectly balanced when I did my first dyno run.

The pair of 39`s shown here have the cable quadrant inboard of the left carb, there are plenty of ways it can be done but I`m not sure how expensive it will all get. The plain alloy spacers and plastic fuel tubes (could be replaced with stainless tube) can all be turned up if you have a lathe handy, even the spindles can be made / machined up but unless you can do it all yourself folks time is expensive:

http://www.sudco.com/Carburetor01.html

on a side note,

has anyone experienced WORN FCR carbs aside from me?
i purchased one of the first WR400 yams into Australia in 1998, FCR carb equipped. After a good deal of use (like a decade) the carb was stuffed. The little wheels on the slide had worn grooves in the carb body and wouldnt allow the slide to bottom out on a reliable basis. The slide still sealed OK, it just stuck above idle speed and made tight riding very tricky.
I sold the bike with a spare carb last year having not ridden it for 5 years, but -is this a common wear point in these FCRs?


Is there a fix?

Well the carb bodies are cast aluminium and those rollers are steel if my memory serves me correctly, (item 20 `roller` as viewed in the exploded view / parts listing in the first of my two links in an above post).
Wear can be expected over a ten year period, the carbs are designed in a way that rollers significantly reduce the rate of wear. Remember with a round slide you have a larger contact area between the slide and carb body so it`s likely not going to wear the carb body and / or slide as fast as will happen with a flat slide carb.
How about Lectron flat slides, were they fitted with rollers?

http://www.ebay.co.uk/itm/Yamaha-TZ250- ... 48448faa2e

I note the Mikuni HSR flatslides have a carb body in two halves, likely so that the slide runner section can be replaced when worn beyond what`s considered useable?

http://www.sudco.com/Diagrams323728/exphsrlate.gif

The rollers on the original FCR slide fitted to the WR400 were solid plastic (dense black) running on shafts directly out of the slide. Perhaps 12mm diameter and 2mm wide.
The wear in the operating area wasnt a big deal, just at idle area. The rollers wore a groove and the radius at the end of the groove would prevent the slide from bottoming reliably.
The inlet vacuum pulses seem to make the situation worse, eventually wearing little spots in the idle area and increasing the force required to pull the slide up.
If given a shake or tap (especially with the engine off) then the slide would revert to its proper idle position via the spring.

It was hard to diagnose as the bike would start and idle, and until wear was very significant, only give me a high idle RIGHT at the wrong moment, (hard braking into a slippery corner then creeping around sort of thing). Note that a high idle on a WR400 in a race is a couple of thousand revs. so- I put it down to a hundred other things first.
There is some sort of seal system (running on dodgy memory here) that allowed the slide to remain sealed in the middle despite how far off the "bore" it was.

I write all this as info for anyone chasing similar idle problems running FCRs, also hoping Keihin came up with a fix as I couldn't figure one.