Amazing ! Clearly explained ! I was lost about lean conditions at slow work on my 450, almost completely lost between hot and cold start, and thanks to you I discovered I switched hot and cold start valve on my FCR41 !!! That explain and make sense with issues I’m facing. Really nice video, best one on KZfaq !

This is by far the best video and information in general I have ever come across about FCR carbs and I have done a ton of research in the last few years so kudos to you for making it and whoever gave this a thumbs down must have not been very intelligent and probably couldn't follow it. In order to learn how to do something good you need to have an understanding of how it works first and this is what you showed us in the video and I'm sure it will help me be a better tuner. I have been switching my bike between stock and a big bore kit and also from both of those to a high compression piston and each time I have to make jetting changes. My bike ran perfect with the stock piston but ever since adding the HC piston I'm having a hard time getting it dialed perfectly in. I finally have it almost there but I'm still getting some weird surging idle. I have changed every jet and tried dozens of combinations and also rebuilt the acc pump diaphragm which helped with an off idle bog I was getting when twisting the throttle fast but the weird surge is still there slightly. It gets better if I turn down the idle but then the bike is hard to get started when hot and also stalls occasionally. I also noticed if I tilt the bike on it's side while it's doing it it goes away. And lastly it gets only noticeable when the bike gets real hot so after running for a good amount of time straight. It seems like the very very slightest twist of the idle makes huge changes so it's hard to get it dialed in. Any help would be appreciated? Thanks again for the video!

this has got to be the best, most in depth FCR explanation I have seen. I need to tune my carb on my KTM and this is perfect info

Thank you Neal. I have had so many people tell me bits and pieces of information about how to tune a mx carb, but no one has ever been able to give me the whole picture. This is very informative and well done. Cheers brother!

Thanks for taking the time to put this together. I've been trying to fix a 10% throttle hiccup on my 525SMR and this is the first mention I've seen of emulsion tube and/or metering rod wear.

The biggest thing I learned from this is I need an AFR gauge. Of the dozens of jetting guides I've seen, none mention this very helpful tool. Seems like everything else is guesswork and an art. Thanks for the tips!

Love it. I have 4 CRF250R (2006-2007-2008) and they all need a bit of love in the carb tuning area. Very well done and concise. Thank you!

I have to agree with all of the comments - incredibly informative video about carburetors and fuel/air flow. I learned more from this video than any other!! THANK YOU for making and sharing it.

Finally found someone who can explain a carby in a way anyone can understand, thank you.

You know what man, 5 years ago I custom built a big 650 single with an FCR from scratch with no baseline for jets. Took me weeks and a lot of angry neighbours! I then shortly after got squashed by a kid in a new car and the bike has sat in the garage since. Well iv decided to look at fixing and completely forgotten the jetting orders, in fact was even scared pulling the carb apart. This vid has instantly refreshed my memory, no bullshit, no unnecessary chit chat, straight to the point with all details covered. For what's it's worth here's one random guy on the Internet who is extremely grateful for your time. Now to see if the beast still has a heartbeat... And annoy the neighbours some. Hopefully.

This video sets the standard for knowledge level for pumper (FCR) carbs. Bravo. 👏

Great video man…super well done!!! I really appreciated your well researched, methodical, and scholarly approach you used with the mechanical drawings while explaining the carburetor circuits and carb tuning theory. Everything you said made 100% sense once you explained everything. This video is a great resource and I’m sure I’ll end up coming back to it a few times as I jet bikes in the future. 🤙

Awesome video brotha jetting was totally confusing, this cleared up a heck of a lot. Thanks for taking the time to put it together.

This a fantastic video. Really great explanation and very well filmed. Thank you for taking the time to put out such an awesome video!

Great video and visual imaging! Thanks for making it easy to understand. Great Work.

Neil... You Are My HERO!!!!! You just saved me months of research! Thanks Brother!

Great video for someone who has no clue about these carbs. I like the cutaway diagram showing fuel and air flow, awesome documentation to have!

Oh and special thanks for explaining the leak jet! I had a pretty good idea how the rest works cause I had a shit time trying to figure out why my yz450 was hard to start and then run like crap and overheat so I've spent a bit of time puzzling over that same style carburettor. But the leak jet was still a mystery to me till now. My problem ended up being a leaking hot start plunger.... I hope! I'm still putting it back together, good video 👍

Great Video!!! Hands down best FCR carb video I've seen yet.

5 year old video and still getting good info from it props for putting together such an informative vid learned a lot

best carb video on KZfaq 👍

Good job explaining all that, good diagrams, thorough, easy to understand, thumbs up.

Well done. Thank you!!! To get more views, you might want to tag 250 four strokes and maybe Keihin FCR carburetor. I've been searching for a video like this for months. YOU have delivered. Great stuff.

Dang great rundown. Helping me get more In depth with the carb. Thank you!

EXCELLENT video. Thanks for taking the time to produce it and post.

One of the best carb videos I have seen yet

with the throttle closed you have high manifold vacuum and it does pull a lot of air threw the "air pilot, air screw as you referred". also the jets do have overlap and for a street conversion sometimes the key can be in the overlap and the right needle is very important for cruising. very nice explanation.

Looks like this became an obsession to get the CRF running as perfectly as possible given changing weather and atmospherics and to understand exactly what was going on in the carb at different throttle openings. Very well explained and logical approach, the overlaying of the jets on the scale diagrams added to the clear and thorough presentation as did the photographs of the worn parts. Excellent educational video, well paced and presented. Would be interested to see how you mounted the sensor probe?

Very educated look inside the workings of the carb and well explained! Good job on the research and details. Thanks!

Awesome presentation man.. I have a major issue with my sm 04 crf450X plated for the street also here in PA. The initial hit on my throttle eyelids a hard bogg but slow increase in throttle it's fine. If my little brain interpreted your information I think I need a smaller leak jet hole. I'm going to make the adjustment and I'll let you know how it works out if you like. Thanks so much for the content man! Your doing great work

I'd agree....great explanation on carb operation and jetting effects!

amazing job! this is incredibly helpful and well done! thank you for doing this tutorial explanation!

best video on this subject i have ever seen. Thank you.

very informative video. well done.I learned a lot that I was not sure of. thanx and keep on riding.

I am very impress with your recaerch and analysis , well don bro

Wow, this is such a great instructional video! I was going to ask the same as a few of the other commenters, is there a pdf copy of the tuning order? I was kind of hoping you would have some other video's of similar nature, I can tell you are a great teacher! 👍

amzing video, really well explained and well thought out. thanks

Wow this is extremely informative.... Very well done 👏

Wow....u are a GOOD TEACHER

Super well done video..Going to help a lot

cheers mate, thank you so much for great info. YT (world) needs you.. dare to say that much!

Awesome video man. helped me troubleshoot the FCR on my YZ250F

How has this not got a million views!

Thank you,after watching the video i menaged to tune the carb properly on my Crf 250r,it was easy to cold start it,usually one kick ,but after the engine warms up it was i nightmare..It was running rich..

Excellent video it's helped my understanding of these carbs

yea this is great. thanks a lot man! just bought a 06 crf450r and i took a vow to never use a mechanic.

Great video. Can you please offer up the reference documents you were using? These look very useful.

Very educational. I run a mikuni tm40 but most of the proces is the same. I consider mounting an AFR gauge myself to finetune

Really good video man....thanks for posting!

such a well informed video on this carb, ive just completed a street legal crf490 build and have been dealing with this nightmare and im bored of having to remove the carb at this point😅 im getting very close but as you say getting the cruise right without hesitation is abit tricky what were the jets and needle specs you ended up with out of interest? also going to get myself an afr gauge so theres no doubt left, ive used afr’s on my cars in the best but didnt think the stock crf electrics would power it.. so good to know this is possible also last thing is could you provide a link to the guide youve made to make the process abit easier when working at the bench cheers for the help, this is an awesome guide

Man, great explanation, how do we get a copy of those documents you put together? Would love to review it for deeper understanding.

Love your detailed explanation. Where do you get the gauge setup and how to connect it to the bike?

Fantastic video. Thanks from Australia

tres bon travail d'explication avec de bons schema, bravo

Great vid. So what would it mean if I have a slight miss fire on the idle AND choke circuit? I waa under the impression that the choke corcuit was its own circuit of air and fuel? When I got this 2006 CRF250R it had a 40 pilot in it has a 172 Main and the needle clip is in the third position from the top. Well I had to go up to a 45 pilot and move the needle clip down to v slot from the top to get it to start and then run smooth at warm up from the idle circuit to the mid-range. Now when I put it on the choke circuit to start it when it's cold there's a slight Miss and then when it's warm it still has the same Miss on the normal idle circuit. I believe that the previous owner put in all balls jetting kit in it because of the number engraved knob headed pilot fuel screw as well as it had a silver number 40 pilot in it. That kit comes with screws pilot jet needle and the adjustment screw for the pilot fuel screw and for carburetor Bowl screws. With a 45 pilot when I screw in the fuel screw at idle after warmed up it will start to die off and stall out and a half Turner below out from seated. But I don't really notice a whole lot more after 2 or two and a half turns out. So I'm contemplating I'm going back to the original stock needle as I'm not sure if this all balls needle is quality enough. You can find a video of my issue on this bike on my channel as it was just uploaded the other day. If you've gotten this far thanks for reading and I look forward to your reply. Andrew C

Awesome video man! What were the main changes that you had to do to your carb for the sumo conversion? Im assuming mainly the needle?

Most detailed FCR video I've seen! Any advice or could you make a video on adjusting the AP timing screw/and leak jet? My ktm 525 bogs a bit off idle and I'm not sure what adjustments to make to help. Cleaned everything and got it spraying/working as it should, just need to fine tune it. 42 pilot, 1-1/8 on air screw as J/D jet kit recommends.

Great video! May I ask where exactly you have welded bung for wideband sensor? How close/far from the engine?

Good video, one of the best I've seen on how a carb works and the air fuel ratio guage was a bonus. I'm looking at purchasing an afr meter to sort out the afr on two of my bikes. I do have a very nice digital carb balancer that has other functions for fine tuning afr etc. but on my v twin its not stable enough to get a steady reading and a colourtune plugh is not fine enough to see the colour change so an afr meter seems to be the way forward?

Thanks for your video Neal. Excellent! I want to try a new emulsion tube in my FCR on my KX450F. On the Kawi parts diagram the only part I can find which might be it, is something they name the "Nozzle main". Part 49121. The main jet screws into it. Is that the emulsion tube?

Excellent detailed video for fcr carb

great video . could you show a close up pic of install location of the meter sensor?

neal, excellent video...i've been fiddly with the carb on my 450x for 6 months...can you tell me where you got those awesome FCR diagrams? i found that the little brass 'ball' that apparently seals the top of the hotstart pathway leaks air and dirt into the carb body....

First Class Explanation!

A+ nicely done! You've save me a lot if time!

I wanted to ask you about something else. Would too small of a main jet affect the slow circuit enough to cause the need of a larger slow jet?

Thanks a lot, my supermoto with a fcr is popping on decel quite a bit trying to figure out why

Great video, super helpful. Show us a video on how to install the air fuel gauge please. Also let me know what model you put on your bike. Everyone will love you for it. I'm assuming you have to weld a thread fitting on to the exhaust pipe to accept the sensor?

Hi, very helpful,One question, if the pilot screw is all screw in, the engine must die?

Great video, good information 👍 thanks for sharing.

Great video! Thanks. Can you give us links to materials and that air fuel gauge setup?

Great video!!! So much useful info

Wow great video. I've been trying to figure my 07 out. Falls flat when I hit wot fast. If I slowly wind it up it's better.

Great video! I just got done putting all the street legal stuff on my 450, and I also live in pa. I go the bike from my brother in Texas, and I was wondering if you could list the jet and needle sizes you used.

Very Very Very GOOD VIDEO !!! Great job , Thanks.

Nice video! Is it normal to block the air jet with your finger while idling and have nothing happen?

Great video. What kind of air fuel meter is that

Huge help. Thank you!

Nice video good job. I need help I got a 2005 crf450x with a big boar 490 what jetting main and low pilot a can put on the bike

Very nice video. How is the AF sensor installed?

I have watched so many vids on how to clean or rebuild these FCR carbs, but very few explain (or do so what any degree competence) what each circuit does with interaction, and what to look for to tune, particularly the air/fuel ratio. And the fyi regarding the emulation tube, and what the hot start does... excellent! I have a few questions: 1- would you post a link to your Tuning Order document? 2- how would elevation affect the air/fuel ratio in terms of target ratios? I'm assuming 12.5 / 13 is still target, just what jets and such it takes to get there would change? (I live at 3k ft and ride between 3k and 9k ft.) 3- what gauge/instrument were you using and how/where did you connect it? I'd love to see a vid on just that :) Thank you for an amazing & very helpful vid.

I have an 08 crf 450r and the previous owner drilled out one of the jets and now it’s very hard to kick start and I have to pull it off to start it with a car and it dosnt idle any tips?

Seriously great work. Thank you!!!

this video is the bomb. badass tutorial. I have learned so much about my own fcr carb now.

I have a trx450er it's pritty moded out, almost everything you can think of including head porting. Recently removed the airbox lid installed a DASA exhaust and switched to a uni filter from a K&N. There is abit of studdering when crusing at 1/2 to 3/4. Dyno jet needle middle clip. Do you think I should raise the needle to rectify this studdering? I'm assuming it's lean now due to the increased air flow. Any ideas for jetting? Thanks

Very, very good video 👍👍

Can I get links for diagrams and schemas ?

Very good, intelligent video! Thanks.

I have a suzuki rmz 450 2007 with the same carb. It was sitting about 1 year.. it did not start.. cleaned the carb twice.. it started but it is running well only with choke on.. when the choke is off the bike popping and backfiring... Also a little smoke comes out from the carb... What is going on????

do you have a link for the pdf file you are holding? that would BE awesome! thanks for the video! so helpful!

Hey man. What Wide Band gage are you using here in your video during the test run? I have a 450X and Id like to install something like that.

Any information on how you added an AFR to your bike? I can't seem to find any info on that with out welding a o2 sensor to your header.

great visual explanation. I have an FCRMX 41 and when I start from 2 turns out and tighten (lean) it revs up all the way till seated. Conversely, if I start from 2 turns out and loosen (richen) it will slow down till it stalls at about 3.5 turns. From what you said, i need a smaller pilot jet. But I just looked at i'm already at 42. I've always run 45 or 48 with other bikes/quads using this carb. Any reason why I might have to go smaller? The carb is from an 07 KTM 450sxf but it's installed on a 2007 Suzuki LTR450 Race quad. (which was injected). Thanks!

We’re did you get that afr gage from. Does it run off a o2 sensor welded to the pipe? Thanks

nice and full explanatory! congrats..

nicely done, explained well!

I have a 04crf450r and when the bike is on gas is coming from the carburetor where the casket sits in the middle where the bottom separates from the top. What do you think the problem is? FYI the gasket is in good condition.

i agree t.. he makes total sense and u can understand

You did an awesome video

How did you accurately measure the float bowl height . did you have a factory gauge or just use a point of reference on the float itself