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Keihin FCR MX 41.5 racing carburetor

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82K views 231 replies 37 participants last post by  flowpro.org 
#1 ·
Freshly rebuild Keihin FCR MX 41.5 racing carburetor for sale,

Assemblies:
- TPS (throttle position sensor)
- Cold start choke
- Hot start choke
- Oversize bowl drain plug
- Fuel mixture screw remote control
- Silicone vent lines + filter case with oiled filter insert
- Velocity stack neck size ø 63.5 mm
- SS bolts

Mods:
- Fuel atomization improving type needle
- High flow main jet
- Air flow velocity increasing plate’s intake side ¼; ½; ¾
- Air/Fuel mixture velocity increasing plate exhaust side ½
- Throttle channel overbore & surface treatment

Jetting specification:
- Needle = OBEPK 3rd middle clip
- Main jet = #175
- Idle jet = #42
- Starter jet = #70
- Leak jet = #65
- Main air jet = #200
- Idle speed air jet = #100
- Fuel mixture screw up to your needs









Price - 320 Eur - worldwide shipped

Any questions............ don't hesitate, contact to me.
 
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#148 · (Edited)





One issue is I need a remote choke cable , no way to ever reach the knob once tank is on , yet another thing these dang bikes are fighting with . But once I get it going and see how she runs I may be in the market for another carb since it fits much, much better than the Lectron without having to make spacers for the tank to sit higher and then everything else that's attached to it only to have the forks hit it on full lock:headshake

Throttle cables need to be about 3/8' longer in the amount sticking out of the sheath , or the outer sheath 3/8" shorter than they are right now . I have both nuts inside the fcr housing right now so only adjustment is one cable up top that is also shortened to the max, but it works right now.

Drain/vent hose should be seperated , the starter and cable is right below and I'm worried about some wearing through or just getting pulled off from being so crunched , the rest fits as good as the stock carb .
 
#150 · (Edited)
Ya, it took a bit but once I got the acc pump primed and could spray gas down the throat it started . Had to turn idle screw a few turns up but now it holds steady at 1700. It seems to be running lean. Even at 65F it needs a few squirts to start and seems a bit sluggish/mild, but at the same time I can tell it has faster throttle response , no bog or hesitation when grabbing a bunch of throttle though. I turned the mixture screw 1.5 turns out(I marked the original spot). Several quick raps to full throttle doesn't give a hint of black smoke , idle sticks a little high for maybe a second then drops right down to 1700.


This one has the stock stuffed up exhaust thus far , I'm trying to find a better performance system but hard to on these oddball bikes, only old stock left. Once a better exhaust is on it I might need more fuel , unfortunately even with the nice main jet access cap, this bike will require total carb removal for any carb work, that damn perimeter frame simply blocks everything.

Is that o-ring mod a good idea for the acc pump ? It helped a lot on my KTM , haven't installed the DRZ carb yet , using it daily and need to get the stroker motor back in it.

Hope to take it out for a road run , it's somewhat icey out since we just had a big snowstorm and this one doesn't go out where it can get damaged , too good of original shape and no new parts available to fix.
 
#151 ·
Does it pops after quick release from WOT?

To solve slight stick of idle just drop down needle by one clip (one click up). It may results as require to add a bit fuel trough idle circuit (add some quarters out for mixture screw if necessary).

O-ring mod makes changes over AP squirt nature. Squirt must be quick, strong and not too long.

What type is your OEM exhaust muffler? More "sleep-on" or regular silent? Installed main jet size is more applicable for "slip-on" type muffler. I'm afraid possible you will be too rich with regular muffler. But, never mind, test ride will show real situation.

Be in touch.
 
#152 · (Edited)
The current exhaust is the stock one , badly choked , wouldn't surprise me if all the mildness is coming from lack of flow through that pipe. I'm going to take the slip-on off the other KLX which is a FMF Mega Max .

Hopefully tonight I can go for a spin , but it may rain/freezing rain by the time I get home for work. It didn't do any popping on decal or anything odd , however that's with no load on the motor thus far , will see on the first ride .


Edit:: Is running just about perfect , started up tonight almost instantly, no squirting, no choke , fired up and went to 1700rpm. Freezing rain prevented any full throttle runs though so a couple days wait. Only had the hang idle at 3000rpm for 1 second then right back down to 1700. stock exhaust yet

.


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#153 · (Edited)
I finally have been able to put some miles on and get it good and warmed up , unfortunately the exact same screaming idle once it is fully warmed up as with the 2 other carbs , this is with the stock low flow exhaust which it should be running rich already. It starts instantly, no choke or acc pump squirt and did it @50ºF when I left it out in the cold , idles @1700 doesn't miss a beat , I can't believe how good it starts. Definitely more power everywhere , it's running perfect as far as I can tell, give her throttle and it takes off hard no bog or stumbles ,let off the throttle and she stays screaming at 3500-4000 as soon as it's warmed up, only when warmed up. Turning down the idle so it idle normal when warm it won't start when cold without holding the throttle open some till it's warmed up otherwise it simply stumbles down and stop from too low idle. This is exactly how they ran with both other carbs I've tried.

I don't think it can be jetted any better really as far as performance ect...however.... I'm going to need to know what is needed to absolutely dump fuel in it to slow it down. Which jets do I need to really go rich, I mean I want it to puff black when I give it throttle , that was the only thing that ever stopped it with my old carb from doing this high idle . My other KLX only gets 33mpg it's jetted so rich and still has the high idle but not quit so bad, was better with 2 sizes bigger pilot , didn't need choke even at 10ºF so it was extremely rich.

Honestly the carb is great , these bikes are just oddballs that don't run normal obviously, there must be something in the design of the head/valves/combustion chamber that simply doesn't allow positive idle both warm and cold ,only can be one or the other to run perfect. I've been referring you to several people looking for an FCR.


.
 
#155 ·
I don't have anything to make a video . Not much to really see , basically when the motor is cold it idles at 1700, as it warms up the idle steadily climbs till it is fully warmed up , it will then be idling at 3500-4000rpm. Tonight as it warmed up I turned the idle screw down , it took about 3 full turns till it would stay at 1700-1750rpm and it would always return there fairly normal riding around for 1/2 hour it always returned to 1700-1750 though a little slower than most bikes . It ran normal and had good power.

From 2000rpm giving it full throttle causes a boggy or lazy takeoff till it hit 3500 roughly , no stumble or hesitation but didn't do much very fast. If I did the same thing when the motor was at 3000-3500rpm already it would take off with authority and accelerate rapidly up to 8000rpm and still going. No popping ever on deceleration, no matter how I did it.

Now with the idle screw turned down so it would idle at a normal rpm when hot it will now start again once cold unless I twist the throttle about 1/8 turn or so and it'll have to stay there till warmed up again. Otherwise it will shut down because of too low idle. This is the exact same thing both KLX's have done with 3 different carbs though this one is running better low/mid to topend and starting with this FCR.

I didn't drop the needle yet , I prefer to change more if I can since it takes an hour to get to the carb so if I need to go bigger on the slow jet ect.. I want to do it all at once. I know 1 item should be changed at a time , but I'm really tired of taking these bikes apart to work on the carbs, not easy.




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#157 ·
I have a relatives wedding this weekend and familt visiting the area so haven't done much but it is running more normal now , the tank vent line which comes out the bottom front of tank(strange setup) and then a hose goes down the front downtube , it melted off because I didn't route it correctly putting it back on when I raised the needle. With the hose cut down and I blew out the vent system, it's now running much better, no high idle like before. Just a little slow returning to idle speed but not bad.

The mixture screw is still out around 5 turns and the needle raised one groove, I was able to turn the idle screw down more and it stays running when cold . I think with one size richer slow fuel jet and it'll be right. Starting it cold it'll idle 1300-1400rpm , fully warmed up 1800-1900.

I'll pm back for any further help to keep this thread from getting offtrack.


I'll be getting another one of these carbs for the other KLX by spring.
 
#159 ·
Carb King Andis

This carb is so beautiful it should be in an art museum, but it looks bad ass on my kX450f. You can really see the craftsmanship.
The modification to the needle is simply amazing. Not only performance wise, but the skill it must have took to drill such precise channels.
The polished aluminum looks simply amazing. Well worth it. Looks super sexy on the bike. It must have took Andis awhile to do.
The velocity stacks are equally impressive. And the machining and welds to hold them in place looks like they were done by a Swiss watch maker.

Performance: My bike never lacked for power, maybe a slight delay in throttle response, but carb seemed fine to me. Man was I wrong! The throttle response on Andis’ carb is incredible. It’s instantaneous. It’s more controllable and responds better to corrections. This alone makes it more than worth it. However, I’ve noticed real gains in performance too. Once I’ve had some more time, and a few races, I’ll give a update review; I have high expectations.

Shipping took about 15 days to KY (South East) US. Not bad at all considering how long it was in NY Customs.

Andis is a carb genius. I am a hobby machinist w/ a lot of experience, but I could not replicate what he’s done with this carb. I’m really proud to own it.
 
#162 ·
Keihin FCR MX 41.75 racing carburettor for KTM 400 / 450 / 505 / 525 / 530. Will fit from 2006 up to 2012.

460 Eur without shipping.

Assemblies:
- TPS (throttle position sensor)
- Cold start choke
- Hot start choke + cable
- Oversize bowl drain plug
- Fuel mixture screw remote control
- R&D power bowl 1 (adjustable leakjet)
- Samco Racing silicone vent lines + filter (Color of hoses (red/yellow/white/blue/green) by your requirement)
- SS bolts
Mods:
- Fuel atomization improving type needle
- High flow main jet
- Air flow velocity increasing plate’s intake side ¼; ½; ¾
- Air/Fuel mixture velocity increasing plate exhaust side ½
- Throttle channel tapered overbore to 41.75 mm
- Throttle channel surface treatment
Jetting specification:
- Needle = OBEKP 3rd middle clip
- Main jet = #178
- Idle jet = #42
- Starter jet = #72







 
#163 ·
I am ready to get the second carb for my other KLX so you can get one going in the spare time so in 2-3 weeks I should be good to go . It'll be nice to have both bikes more ridable finally . Dimension the same as the other but if possible make the air filter intake bell 6-8mm longer than the last one . The boots are old and stiff so they're about that much shrunk down . I had the other one soaking in wintergreen oil to soften it up and it fit good but it won't hurt anything to have the carb helping push the boot into the airbox even more for a good seal. The 4 vent lines going into the filter works, but is a little tight with the starter directly below the bowl , I don't know if you have a 2 line filter and just use 2 of them or if one of those aluminum canisters I've seen on some of yours would maybe work better ???

Jetting specks the same but start with needle raised one notch and slow fuel jet #45 .






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#165 · (Edited)
If the Idle screw and /or mixture screw could be made longer to reach out the side of head as seen in picture below , the bracket for oem idle screw is shown close to camera



The hoses are actually hitting the exhaust because they are being pushed over by the starter and where the positive electrical post is .



Idle adjustment knob could otherwise face out on the exhaust side , very hard to reach it from the other side ,can be seen in picture below V



It may work if the hoses were held to the carb bowl on the left side ( kickstand side as mounted) so they can be routed around the other side of starter electrical wire . Length hanging down could be 2-3inches longer , they end above the swingarm and rear engine mount.

I should have all the $ in a couple weeks so whenever you get it done it'll be fine . Will be nice to have both of these bikes running good and actually very "driveable" .


.
 
#166 ·
If the Idle screw and /or mixture screw could be made longer to reach out the side of head as seen in picture below , the bracket for oem idle screw is shown close to camera

The hoses are actually hitting the exhaust because they are being pushed over by the starter and where the positive electrical post is .

Idle adjustment knob could otherwise face out on the exhaust side , very hard to reach it from the other side ,can be seen in picture below V

It may work if the hoses were held to the carb bowl on the left side ( kickstand side as mounted) so they can be routed around the other side of starter electrical wire . Length hanging down could be 2-3inches longer , they end above the swingarm and rear engine mount.

I should have all the $ in a couple weeks so whenever you get it done it'll be fine . Will be nice to have both of these bikes running good and actually very "driveable" .

.


Alright, I can propose to do so:
- 6-8 mm longer velocity stack isn't a problem, I can made 1-2 mm less OD of it, if wish. According to my opinion it would help with installation.
- mixture screw I can relocate to opposite side, so you can freely reach it
- the only solution for idle speed adjuster is to let it freely hanging at right side, this is the same way like for old carb Husqvarna’s
- to solve vent line filter issue I can leave longer hoses, so you can rote them later on the way fits best of all

Catch tank is possible too, but it will be a bit complex without having bike on site.
 
#167 ·
Keihin FCR MX 41.5 performance carburettor Yamaha YZF WRF 450 up to 2009.

420Eur Worldwide shipped.

Assemblies:
- TPS (throttle position sensor)
- Throttle cables
- Cold start choke
- Hot start choke + cable
- Oversize bowl drain plug
- Fuel mixture screw remote control
- Boyeseen quick shot AP cover
- Samco Racing silicone vent lines + filter
- SS bolts
Mods:
- Fuel atomization improving type needle
- High flow main jet
- Air flow velocity increasing plate’s intake side ¼; ½; ¾
- Air/Fuel mixture velocity increasing plate exhaust side ½
- Throttle channel tapered overbore to 41.5 mm
- Throttle channel surface treatment
Jetting specification:
- Needle = NHFS 3rd middle clip
- Main jet = #170
- Idle jet = #42
- Starter jet = #72






 
#175 ·
Keihin FCR MX 41.7mm. Specially built for "big red hog" Honda XR650.
460 Eur worldwide shipped.

Assemblies:
- Cold start choke
- Oversize bowl drain plug
- Fuel mixture screw remote control
- Silicone vent lines + filter
- SS bolts
Mods:
- Fuel atomization improving type needle
- High flow main jet
- Air flow velocity increasing plate’s intake side ¼; ½; ¾
- Air/Fuel mixture velocity increasing plate exhaust side ½
- Throttle channel tapered overbore to 41.7 mm
- Throttle channel surface treatment
Jetting specification:
- Needle = NCYQ 3rd middle clip
- Main jet = #170
- Idle jet = #45
- Starter jet = #68
- Leak jet = #55
- Slow air jet = #100
- AP rod length = 2.7 mm








 
#177 ·
2008 CRF450R Keihin FCR MX 41.8 Motard trim Plug & Play.
Assemblies:
- TPS (throttle position sensor)
- Cold start choke
- Oversize bowl drain plug
- R&D Powerbowl 1
- Fuel mixture screw remote control
- Samco Racing silicone vent lines
- Custom welded aluminum overflow tank
- SS bolts
Mods:
- Fuel atomization improving type needle
- High flow main jet
- Air flow velocity increasing plate’s intake side ¼; ½; ¾
- Air/Fuel mixture velocity increasing plate exhaust side ½
- Throttle channel tapered overbore
- Throttle channel surface treatment
Jetting specification:
- Needle = DVR 3rd middle clip
- Main jet = #170
- Idle jet = #45
- Starter jet = #68
- Fuel mixture screw up to your needs

500 EUR Worldwide shipped











 
#179 ·
Keihin FCR MX 41.75 KTM LC4 Duke 505 525 530 SMR

450 Eur worldwide shipped.

Assemblies:
- TPS (throttle position sensor)
- Cold start choke
- Hot start choke
- Oversize bowl drain plug
- Fuel mixture screw remote control
- Samco Racing silicone vent lines + filter
- SS bolts
Mods:
- Fuel atomization improving type needle
- High flow main jet
- Air flow velocity increasing plate’s intake side ¼; ½; ¾
- Air/Fuel mixture velocity increasing plate exhaust side ½
- Throttle channel tapered overbore to 41.75 mm
- Throttle channel surface treatment
Jetting specification:
- Needle = OBDVR 3rd middle clip
- Main jet = #170
- Idle jet = #42
- Starter jet = #72
- Leak jet = #60
- Main air jet = #200
- Slow air jet = #100













 
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