Keihin FCR 41 MK1 / Mk2????? explain/ jetting for FS 600

croo · May 19, 2008

Hello everybody,

its my first post here as an user, im reading sometimes here some useful help.

But I have a problem wich I want to clear.
I bought not long ago a keihin FCR 41 carburator, on ebay form USA.

Now ive mounted it already on my bike but it doesnt run "smoothley" or just rare.
I even dont know what kind of carb it is!!! I know only there are some different carbs out there.
Thats why im asking here for help, maybe some ppl have the same carb on a FS 650.
Im driving a FS 600 '98

Here are a few pictures of it:

Ive removed the remote hot start cable, now is there just a small hole left, does this affect the driving?!

This fits okay right?dont look at the screws or whatever from the throttlecable, they are too short for now, but first I want that the carb works well. I demounted the plastic on the photo advised

Its still the same "intakenipple" from the PHM 40

And how about this one?! The "Adapter" is looking a bit more out:

I will take out the carb now, and see what jets/needle are currently mounted.

I hope you can give me a small input to this carb and tell me the most important things of it.

And im sorry for my bad english, im trying my best to make it understandable. And I apologize for the photoquality

greetings
croo :evil:

Taffy · May 19, 2008

the only photo you didn't take was the one from the entrance!

you need to get a luittle closer. the carb looks like a Mk2 MX which is good. but that belmouth? please remove it and let us see the catrb without this.

regards

Taffy

buckwheat5679 · May 19, 2008

On the end of the hot start cable that connects to the carb there is a brass tip and a spring, do you have that installed in the carb to seal off the hole?
If not you will have a large air leak and cause it to be very lean.

croo · May 20, 2008

Re: RE: Keihin FCR 41 MK1 / Mk2????? explain/ jetting for FS

Taffy said:
the only photo you didn't take was the one from the entrance!

you need to get a luittle closer. the carb looks like a Mk2 MX which is good. but that belmouth? please remove it and let us see the catrb without this.

regards

Taffy

okay, good to hear that Ill remove it immediately, just came home from work.

buckwheat5679 said:
On the end of the hot start cable that connects to the carb there is a brass tip and a spring, do you have that installed in the carb to seal off the hole?
If not you will have a large air leak and cause it to be very lean.

Yes there was a spring, Ive installed it there, but still during the drivin I think the carb gets air from somewhere. Didnt figure it out till now. Now Ive taped it and will see at the next test how it works.

thanks for the quick responses

croo · May 20, 2008

RE: Re: RE: Keihin FCR 41 MK1 / Mk2????? explain/ jetting fo

hmm the screws are really tighty, have to wait anotherday, till Im at my workplace where I have the right equipment to demount it.

But for what is this belmouth and what does it do?

And do you have any Idea about the probably right jetsetup?

Greetings

p.S and do you guys know with throttlegrip or however this is called, fits to this carb? I even dont know from wich bike it is!

I am badly unlucky with this I think

croo · May 20, 2008

RE: Re: RE: Keihin FCR 41 MK1 / Mk2????? explain/ jetting fo

hmm okay guys, I see I replie only to myselfe hehe :roll:

I cant demount the bellmouth , I dont have any screws or something, just a small hole at 3 o clock thats all, if someone know how to demount it, write it
here or pm!

Ive found out the jettings on it.

Needle is an OBEKR
Mainjet: 170
Pilotjet: 45
Startjet: 72
slowairjet: 100
mainairjet : missing

Does this looks fine?

greetings

whosahberg · May 21, 2008

greetings sir .. it is a bit of a risk getting a carb off ebay , i have heard and seen some horror stories . i hope you sort this one out :wink:

in some cases people remove the main air jet

croo · May 21, 2008

what effect do you get out from it?! And for whats the "bellmouth" nessecary ???

greetings
alex

Taffy · May 21, 2008

you should still have the thread for a MAJ? right?

it adds air at high revs to the mixture. belmouth 'lines up' the air at low speeds to stop a hesitancy.

regards

Taffy

croo · May 22, 2008

yeah I still have the thread for the MAJ, on 2/4 throttle I have a bird tweet sound, this is maybe there because the adapter is longer then the back flange. And there are maybe some curl cause of that. Or its because of the missing MAJ, or the missing remote-hotstart bowdenpusher.

I dont know, ive tested the machine today, and I have to say WoooW insane how it works

I just need to change the needle and then it will be alright.

greetings
alex

ned37 · May 23, 2008

on 2/4 throttle I have a bird tweet sound

thats normal for a berg with a flatslide carb.

croo · May 23, 2008

okay, didnt know it, was just wondering about it!

I think the thread can be closed, I just didnt find out how to demount the belmouth but doesnt matter anymore hehe.

What about the cylinderflange? Do I haVe to change it to an orginal one from KEIHIN, or is the one from the PHM 40 dellorto okay?

greetings
aleX

Taffy · May 24, 2008

take the last 5mm off and the keihin will fit onto the lip perfectly!

regards

Taffy

Dudemeister · Oct 27, 2010

(I know this is an old thread - but I came across it and wanted to give the proper info)

This is a Keihin FCR MX 40 - from a 2002 - 2004 Honda CRF450R.
It's not a 41 mm carb (Honda only put 41mm carbs on the 07/08 CRF450R).

If you want to measure the carb, measure the venturi at the throttle slide (which is at the smallest diameter). A common mistake is to measure at the intake or outlet of the carb - which will off course yield a larger measurement (much used by eBay sellers...).

Keihin FCR 41 MK1 / Mk2????? explain/ jetting for FS 600

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