• There has been a recent cluster of spammers accessing BARFer accounts and posting spam. To safeguard your account, please consider changing your password. It would be even better to take the additional step of enabling 2 Factor Authentication (2FA) on your BARF account. Read more here.

fcr 39 troubles

auntiebling

auntiebling

megalomaniacal troglodyte
Super Moderator
Joined
Apr 27, 2004
Location
atop the parapet
Moto(s)
.
i have an fcr39 on a ktm lc4 400. it is a bitch to get started (kick only, might be technique issues), will not idle but seems fine at Really Loud RPMs, say half throttle and more.

i've been internetting, and found this:

2) Idle

Set idle speed to proper r.p.m, by adjusting the IDLE SPEED SCREW. Turn the IDLE MIXTURE SCREW or the AIR SCREW to for correct procedure, achieve highest speed and best response. The IDLE MIXTURE SCREW (FCR) controls fuel delivery to the idle port and the SCREW is located on the engine side of the carburetor slide. Turning the IDLE MIXTURE SCREW out will make idle and off-idle richer. Turning IDLE MIXTURE SCREW (CR, PWK, PJ, PE) controls the amount of air to the IDLE and SLOW CIRCUIT. This SCREW is located on the air cleaner side of the throttle slide and turning the SCREW out will lean the mixture and turning the SCREW in (clockwise) will richen the mixture.
Click to expand...
from carbparts.com

they indicate that there is an idle mixture screw that is not the famous Fuel Screw, nor is it the thumb screw flexy shaft that sets idle speed via opening the slide slightly.

i can't find a picture of this screw, and don't have the carb in front of me to hypothesize. does anyone know where i should be looking? "engine side of the carburetor slide" is still pretty vague
 
the only other screw that does anything tuning wise is the accel pump duration screw, located by the throttle wheel. if it was mine i'd double check the fuel/air screw & the accel pump screw & make sure no ones been adjusting them for more powah! stock spec is always a good baseline to start with.
 
http://www.sudco.com/Diagrams123/expfcrmx.gif
Eh?

Is the bike a bitch to get started cold? hot? Won't idle and sounds okay at high throttle sounds like it's running too lean, how's the plug look?

I think I would check the Air/Fuel mixture screw (the right one, not the idle one), for proper adjustment (I'd just emulate the DRZ400 specs and tune from there), and then check to see where idle is at.
I guess you could also just turn the idle adjustment up pretty high and see if it'll help.
 
Hybridchemistry said:
http://www.sudco.com/Diagrams123/expfcrmx.gif
Eh?
Click to expand...
seen that, don't see the "engine side screw" referenced above.

i believe 32 is the only thing i've diddled. i got the bike at 4.5 turns out, reset to 3.5 per internet wisdom and stan23

Is the bike a bitch to get started cold? hot? Won't idle and sounds okay at high throttle sounds like it's running too lean, how's the plug look?
Click to expand...
-yes
-haven't run it long enough to get warm
-correct, won't idle at all
-high throttle sounds loud as fuck.
-haven't checked plug, would be kinda worthless without some baseline runtime (at least as far as i understand plug reading goes)

I think I would check the Air/Fuel mixture screw (the right one, not the idle one), for proper adjustment (I'd just emulate the DRZ400 specs and tune from there), and then check to see where idle is at.
I guess you could also just turn the idle adjustment up pretty high and see if it'll help.
Click to expand...

which part number are you referring to for mixture screws. from my reading an FCR has a fuel screw (the aforementioned #32 i think) and an air screw... somewhere

i've tried turning the idle adjustment thingy all the way up (#90), made no impact.
 
i've never seen the idle mixture screw on the FCR. Just like skippy says, there's only 3 adjustable points. The fuel screw, the AP, and the idle knob. The AP is only useful for the timing between twisting the throttle and the squirt duration.

you know, the valves could be off or timing, and that would result in hard starting and not running at idle. you remember my husky when it jumped time!?

You can also call and talk to the guys at zoom cycle. They are a wealth of knowledge when it comes to carbs. Just buy some jets or something.
 
Last edited:
you didn't clean out hte pilot first?? it's #32. That would've been the first thing I would do. That controls idle and low throttle - i believe.
 
BTW, I had one DRZ with a perfectly setup fcr39.

I buy another DRZ and a brand new FCR from sudco, and had lot's of problems getting it jetted correctly. I would get idle hangs.

Anyways, just wondering this since your bike came with a spare FCR, maybe the PO had issues too and though it to be the carb?
 
I cleaned the bowl and prayed

The spare fcr reportedly has some stripped jet threads, and is missing some of said jets which was a large source of many questions I asked you.

I think I can just rotate the carb tongain access now, instead of taking half the bike apart, so this might even get looked at before summer ends!
 
If someone brought me this bike the first thing I'd do is check the valves and hope it was that; and then next thing I'd hope for was an air leak.. :laughing
 
Ironbutt said:
If someone brought me this bike the first thing I'd do is check the valves and hope it was that; and then next thing I'd hope for was an air leak.. :laughing
Click to expand...

I resemble that remark :twofinger :rofl

Chad is spot on. New to you bike, check valves, clean carb (not just float bowl - but actually remove pilot), and check for leaks.

Just dont talk about a particular XR or I might go into a historamic fit. :teeth
 
Having recently been through the FCR dance, I would refer you to the excellent Factorypro article on the topic.

A couple things:
1) There is both an air screw and a fuel screw which have the opposite effect on the idle circuit (in on the air screw is more rich, in on the fuel screw is more lean). The air screw is located in the throat of the intake side.

fcr_face.jpg

A in this photo

Look at the factorypro chart, the air screw is extremely sensitive. A small fraction of a turn is like changing your slow air jet several sizes.

2) You can disable the accelerator pump to test if you think that is an issue, but if you can both snap the throttle open as well as hold constant throttle without issue, it is an unlikely culprit.

3) I would definitely begin by diagnosing in this order:
- Air leaks
- Clean carbs
- Float height
- Mixture screws
- Needle taper/height
- Jet sizes
- Valves, etc.

This depends on your knowledge of the bike's condition, such as ignition system being 100% and whatnot.

4) Think about what needle you are running. To quote factorypro:

3rd letter: This portion of the needle has the greatest effect on mixture between closed and 1/4 throttle. If the engine is too rich while gradually accelerating through 1/8 throttle, select a needle with a larger root diameter. If the engine is too lean when gradually accelerating through 1/8 throttle, select a needle with a smaller root diameter. You will drive yourself completely batty trying to sort out this if the slow fuel and air jets aren't right. Conversely, you will drive yourself completely batty if you try to sort out the slow fuel and air jets if the needle root diameter isn't right. So you're pretty much screwed either way here. And if you didn't set the float level to 9mm, just go jump off a cliff right now and get it over with because that will have a fairly large effect on how much fuel spurts up through the needle jet when the slide's only open a little bit.
Click to expand...

Neat carbs though.
 
First off that article by Patrick Burns on tuning the FCR's is the shiznit. When I tuned my M900 nobody could seem to help because it has a RoadRacing exhaust (rather rare) and pod filters. That article got me on the paper so I could get some traction. I was two needles away from what the "experts" recommended in the end. Runs GREAT.

Second I suggest you try the DRZ400 setup. I have also found the internet experts to be wrong on this jetting for my application and have verified it on another similar equipped bike. Setup is for full aftermarket exhaust (in one case full Yoshimura and other case full FMF PowerBomb and Q2 pipe) as well as "3x3 mod" (opened up airbox). The setup that works well is as follows:
-EMN needle
-Needle on 5th clip (from top)
-165 main jet
-45 pilot jet
-200 Main Air jet
-Slow air jet left in as equipped (can't remember size right now)
-AP (accelerator pump) screw backed out almost all the way
-About one turn out on the idle mix screw. You can kill it from idle by closing it. See the article by Patrick on this works great.
With this setup I can pull well all the way to redline and there is very little pop on decel with the throttle partial or closed. I run from sea level to about 2500 feet locally and it's good all over. I expect to run a 162/160 main and possibly go to 4th clip at higher elevations more testing later this year when I get into the Sierras with it. No doubt I'll be bringing an assortment along with an EMP needle. I haven't found it necessary to do the "o-ring mod" to the AP yet but can't see how it would hurt. More testing in the works....

Last of course what the other guys have mentioned. Valve adjustments and stuff otherwise your pissing in the wind. Hopefully this gets you on the paper at the range. Once your there it gets a LOT easier but I can relate to being way off target and going batshit with it. Best of luck.
 
none more black knows the FCR. There is an idle adjustment, an adjustable air screw, top next to the intake and paired with another jet, and on the bottom the fuel screw at the bottom of an inch deep well. If it won't idle, try the idle screw first ( the flexy thingy)
 
Probably worth checking to see the condition of the slide and vacuum plate as well as vacuum plate o-ring. That can cause a pretty good leak
 
You must log in or register to reply here.
Back
Top