Keihin FCR Vacuum Release Plate & Seal

The Keihin FCR-MX Carbs are notorious for having this plate wear / crack / rattle etc....

To buy the plate and the seal is an excercise in frustration when it comes to the pricing that gets quoted around the place. The way to go is this: Buy the Honda 'kit' which comprises the seal and the plate for around $64.00 + shipping. The Honda part number is 16037-MEB-671 . To buy the parts here in Oz (as a genuine Honda part) will set you back around $214.00 retail so make sure you go to a US Honda parts supplier.

Before you start the job (giving the carb a birthday) it's worth having a read of this: http://www.dirtrider.com/features/protips/141_0707_keihin_fcr_carb_rebuild/

Cheers,
Bushpig

Hi and welcome

There is another problem, even if you have a new plate and seal you can also have grooves on body were the wheels work, so even with a new plate and seal you can have too much gap between the plate and the body, so you will have one intake of air uncontroled, that is leaning your mixture.

Here one example from me:
[attachment=1:29h5418z]FCR_Body_Grooves.jpg[/attachment:29h5418z]

I have repaired that grooves but probably did not done a good job, because I still have more gap than I wich, then I tryed to make a different seal but could not done it, its very dificult, I had to make one mould and its too expensive to do it for one piece.
Now I'm playing with gaskets, here is a pict:
[attachment=0:29h5418z]Plate_gasket.jpg[/attachment:29h5418z]
This is a gasket with metal inside to not be compress by the presure, it happens.

This is one ongoing job, will try to develop the idea.

:cheers:
ZAGA

Correct. There's only one (of two) wear related problems being addressed by replacing the plate & seal, but they do need replacing.

Your photo shows the grooving really well, and unless they've seen it for themselves many people just don't believe it's an issue. I've heard of people filling them (the grooves) with Devcon and all sorts of other things but there has to be a better way but I'm just not sure what it is. No doubt someone will come up with a fix, and when they do......

Cheers,
Bushpig

Hi

I don't know a better way, that is how I've done it:
[attachment=2:3c5t876y]FCR_body_repair_1.jpg[/attachment:3c5t876y]
[attachment=1:3c5t876y]FCR_body_repair_2.jpg[/attachment:3c5t876y]

Then I used a file and many hours
I've used DEVCON clear epoxi and the plastic steel, the plastic steel its easier to work but the clear epoxi its lasting more (I think)

[attachment=0:3c5t876y]Devcon_2 Ton Epoxy_1.jpg[/attachment:3c5t876y]

If you find other way, let me know

:cheers:
ZAGA

Gentlemen,
I have yet to experience this joy.

Thinking laterally, what would happen if the wheels were of slightly larger diameter to compensate for the wear? It's possible the grooves will be too uneven for this to work, but if it did it would be a far easier job to make some oversize wheels.

Cheers... Paul

Hi Paul

That was one of my first thoughts, but unfortunatly no, that is not the solution.

The thing is, you want the slide and most important the plate to go to the front of the carb (engine side) so it will be agaist be body carb. By doing this you will seal all other intakes of air from the top of the carb. The only air you want in, is the one you control, wich is the one that goes underneath the slide, by normal intake process.

In a new carb you have a very little gap, and that gap is compensated by the seal that act as a spring, keeping the plate allways against the carb body.

What I've tryed to do was a rubber seal that was a spring with more range to compensate the wear, but its realy hard to do, only if I made a mould to do it, for now I'm using a gasket to limit the travel of plate, because I don't want to do the epoxi thing again, I just don't have the patience to go all over again

:cheers:
ZAGA

hi zaga

good to see you having more understanding about my new mod, maybe i should try to explain as i have used this mod for many hours on my bike.
first of all i was having problems with the fcr it had an unpredictable idle, sometimes when you shut off the idle would stay high then sometimes it would idle perfect then other times it would drop to nothing and stall.
when the bike was off idle it was great but i ride motox and i ride hard so this was a problem as its near impossible to hit the same lines on every lap with a wild idle, so i started researching and found the problem with the slide wheels wearing away the carb body so i stripped the carb down to ***** the damage .
after looking at the grooves that the wheels had made i decided that filling them with some kind of epoxy was not for me! what if the epoxy came loose and jammed the slide open ?? i would end up with some serious injuries.

i also own a mk1 fcr so i stripped this down to make some comparisons, i found hardly any wear at all so i took all the wheels off both slides so i could get a more accurate reading of slide to body clearance, i found my problematic mk2 had some 0.5mm more clearance than my mk1.

i tried swapping the rubber seals from under the slide plate with no improvement , so i measured how much the plate sat away from the slide with the rubber seal in place it was 0.3mm , i then made a new seal i had no rubber so i used good quality gasket paper i used 0.8mm as this was 0.5mm thicker .
i fitted the plate back on the slide then back in the carb it looked perfect not tight at all but not too much clearance either. i fitted my fcr back on my bike and she runs like a dream drops to the same idle every time with out fail .

but after many outings and many hard hours of riding my crazy idle started coming back , so i stripped the carb again to find that the gasket i had made had been compressed by the induction force, so i then came up with another idea i thought what if i used a thicker gasket but pre compressed it in the press before fitting??

unfortunatly i dont have the right thickness gasket paper here to make a new 1 and i have had no time to pick some up but i am very confident that when i do it will work just as amazingly for a lot longer or forever ( i wish lol ).

so for the price of a piece of gasket paper smaller than a credit card its well worth a try

cheers kris

kris,
why not use a piece of brass or steel shim of the required thickness? Easy to get, available in very small thickness increments, cheap and will not compress.
Just a thought.

Thanks for the excellent description of your solution by the way.

Cheers... Paul

hi paul

the original rubber seal behind the plate is a stretch fit as in it has to sit under a lip and if i had used a piece of metal of some kind i would never have got it to fit as metal will stretch but not spring back like gasket paper.

the 0.8mm gasket i made lasted for many rides the crazy idle did come back as the gasket compressed but it still was not as bad as without it .
so i got 15-20 riding hours before it compressed , now i am definatly thinking that if i use 1.2/1.3mm gasket paper and pre compress to my desired 0.8 that the 15-20 hours could well turn into 150-200 hours.
i bought my fcr cheap with this idle issue i payyed £120 for it but it was fully kitted out with all of taffys best bits which alone would cost around what payyed for the whole package and after stumbling upon this very easy cheap mod my carb has gone from ready for the bin to ready for racing , the jetting kit and super needle is working very nice and the carb conversion has made my 650 the ultimate off roader .

cheers kris

Hi all

None of this solutions are excelent ones, the excelent was to have a new carb but as kris pointed this is a very expensive piece, and like him I bought mine used and cheap and spent the same also with Taffys bits.

The thing is, I would not advice the gasket alone like a fix, because I don't think the wear grooves are even, but I'm not shure, and when the seal is enough to fill the gap it can compesate the uneven wear because it act as a sring all the way arround the plate. I think the grooves are deeper on the bottom of the carb because its there that it spends more time and is when it is exposed to more pressure (don't know if I explained well ??).

Anyway if we don't have the coins for a new one, we have to find some kind of fix Now I'm thinking of a teflon shim that you can cut with a lathe and might be a more durable fix, that won't compress.

Kris I will send you one of my gaskets, it has metal inside and it won't compress as easy, for you to try.

:cheers:
ZAGA

Hi again

I've made a search on the web and didn't found any solutions, but found some aftermarket plates that you might be interested:

[attachment=2:3bdbjte3]FCRslides.jpg[/attachment:3bdbjte3]
This ones came from ebay and were at $60, but it ended

[attachment=1:3bdbjte3]1940.jpg[/attachment:3bdbjte3]
[attachment=0:3bdbjte3]1939.jpg[/attachment:3bdbjte3]
This ones are from keihin.de and I think its arround 140eur

They both claim that they are stronger than the original.

:cheers:
ZAGA

Gents, an interesting thread with ideas for the same problem I am experiencing. I'd like to see a photo of the gasket solution as it's not clear to me.
If I understand correctly, the following is the effect of wear form the rollers:

under suction the slide can move further forward onto the carb body and press the plate harder against the wall of the carb body? on my carb the grooves are deep enough that now the slide itself touches the front of the carb body, i can see the wear marks. The whole slide must rock forwards at the bottom according to the wear marks on the bottom front side of my throttle plate.

in the normal condition without any wear, then the slide must sit further back from the front face and have more clearance. The throttle plate must be able to move further forward away from the slide body and against the carb face when new?

One possible, "easy" solution I can see is to make new wheels from a plastic material that are wider, sitting further in towards each side of the slide, so that they will run over the previously unworn section of the carb body. I think we can get 1.5mm in this way. Thoughts please?

Just come in from the cave. having stripped the bottom half off the body of the carb.
The wear on mine is deep enough at the bottom that the slide can now contact the carb body.

The wheels can be redesigned to sit very close to the slide body, inwards, getting another 1.5mm of load bearing surface, a good idea anyway to reduce wear, even on a carb that is in good condition today.

I'm taking the body to a friend tomorrow and see what his thoughts are about wire EDM a channel, idea from earlier in this thread, from the inside corner of the carb to just past the wear zone, on all 4 corners. Keeping depth to a minimum to get rid of say 75% of the groove depths. Then we insert some brass strips up all 4 sides. Need to give some thought as to how to secure the brass strip, as it will be less than 1mm in thickness, but I'm sure there's some glue / resin / epoxy out there that's more than capable.

If this seems to be a goer, then since most of these carb bodies are from the same casting, it should be possible to repair the majority like this using the same fixture.

The replacement wheels should be made from a softer sacrificial material and cost only pence each, so easy to have 20 in a bag and replace all 4 each year. Would this not be a way forward for new carburettors?

Any thoughts?

sounds good

i like the idea of brass or steel inserts, possibly the job can be done by a good machinist without edm in case access to such a machine is difficult .. not the case for you probably but others.

none of my carbs have ever worn out so i cant offer much advice sorry, i use caltex vortex 98 and there always seems to be an oily residue in the top of the carb and on the slide

did you notice one wheel is smaller intentionally so that the slide sits on 3 points rather than try to be on 4 ?

Thanks for this info. Am I the only one who really appreciates that this board gives like this, but remain unsure I even understand it all?

Bushpig said:

The Keihin FCR-MX Carbs are notorious for having this plate wear / crack / rattle etc....

To buy the plate and the seal is an excercise in frustration when it comes to the pricing that gets quoted around the place. The way to go is this: Buy the Honda 'kit' which comprises the seal and the plate for around $64.00 + shipping. The Honda part number is 16037-MEB-671 . To buy the parts here in Oz (as a genuine Honda part) will set you back around $214.00 retail so make sure you go to a US Honda parts supplier.

Before you start the job (giving the carb a birthday) it's worth having a read of this: The Keihin FCR Carb Rebuild With Zip-Ty Racing - Dr. Dirt - Dirt Rider Magazine | Dirt Rider

Cheers,
Bushpig

Click to expand...

I just ordered the Husaberg/KTM gasket kit 57331099000 which includes the Vacuum Release Plate Seal, all gaskets and O-rings, except the mid body seal, for about $90.00. Also ordered the needle valve assembly 57331020000 for $70.00. The Husaberg exploded diagram does not contain part numbers for all of the parts shown. I could only find the tiny torx screw that holds the link arm to the slide from Sudco. I thought the torx was a Phillips and ruined it in no time. Their exploded diagram seems to show all of the parts except the mid-body gasket that is only available from Athena I believe.

Once I dismount the carb yet once again ( I am actually getting good at removing and installing it so something good is coming out of this) and install all of these parts hopefully it will cure the massive exodus of fuel from the overflow and bottom of the carb. I will definitely check for body grooving and release plate wear.

Stage 1 Completed

Ok, as mentioned last night, took the carb body with drawing to an EDM shop today and they performed their magic.
The attached photos show a 6mm wide channel that is 0.8mm deep, wire eroded out of the wear areas. A quick and pain free exercise.
If I was to do again, I would get him to take back the front face of the carb body by maybe 0.2mm to get rid of the majority of the wear present on it.
A new throttle plate could be made that is thicker by the same value to compensate and keep the clearances the same.

Next step is to cut the insert strips and these will be made with 0.8mm stainless steel. They will be fettled to a good press fit and bonded into place. Any unevenness will be made good with light stoning to leave a flat surface.

It'll be a week or 2, maybe into Christmas before I get this completed and tested, but I'll report back as I make progress.

For anyone without a worn carb I would strongly urge to replace the wheels with ones that are 1mm wider and from a softer material. If there was enough volume I'd think these would become only a couple of quid each. The Keihin item is £8 in the UK. These could then be replaced every year and there will be no future issue with carb wear. I'll get some made and let you all have a look and think.


If I'm missing anything, please shout before I go flat in 6th over a cliff edge

Cheers

Gavin


P.S. Photos to follow, looks like I have to upload them first ......gggrrrrrrr

Just a thought before I forget. How about fitting a sleeve made of Nylatron. This stuff wears like iron and is self dry lubricating. Of course this would not be a do-it-yourself operation but if someone is thinking about bringing a commercial fix to market............

Nylatron NSM self lubricating, highest wear resistant, nylon plastic for bearing aplications such as, wear pads, linear pads, rollers, wheels, wear components, gears - Quadrant

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