FCR Carb Accelerator Pump Tuning [EXPLAINED]

How to adjust the accelerator pump on a Kehin FCR Carburetor.
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[@mitaux495]

Thank you, explained in a very good way!!!

[@user-di3yt6qy4f]

FANTASTIC EXPLANATION OF HOW THIS SHOULD BE SET UP! ON OTHER FCR MX VIDEOS, THE AIR CUT OFF DIAPHRAGM IS MISSING ALTOGETHER!!! WHY WOULD THIS BE? TANX

[@lostcoastliquid3490]

Thank you! I have been helping a buddy tune his yz250f. I cleaned all the jets and made sure the whole carb was operating properly. Still bogging off the bottom when the throttle is opened quickly. I’m pretty sure the AP is the culprit. He’s already stoked because the bike is running better than ever but that bog is not cash money.

[@madjack_757]

Right on man! Im glad this video is helping you guys get that bike ripping again 🤟🤟

[@jettjensen4902]

Talk about an extremely helpful video!!! Thanks big time!

[@madjack_757]

Glad it helped!

[@luckyaffpv343]

Not enough likes. This video is great Amazing demo. Thanks keep up the good work

[@madjack_757]

Thanks so much man! I hope it helps everyone with carb issues cuz carbs can be a struggle sometimes lol

[@mxriderwd]

Great video

[@reeceparlato6574]

1st person i have seen exsplain this so well

[@madjack_757]

thank you!

[@tylermiller8525]

first off great vid! second i have a 2003 yamaha yz250f that im having some issues with the carb i bought a brand new one from RMATV and im getting spitting and sputtering in the mid range and can not get it figured out. WOT it does not happen also with the old carb it dosent do it either reason for chaning is sticky slide and broken off fuel screw along with a bunch of stripped out screws! any help would be greatly appreciated!

[@madjack_757]

Hey Tyler, by any chance have you checked your spark plug?

[@juzt2fresh86]

Hey great video quick question I’m getting a leak right at the accelerator pump when I open and close the throttle some fuel squirts out of that area and down the carb I located it to there and tested it any ideas I’m new to carbs

[@madjack_757]

Yeah that will definitely hurt the performance of your bike. I would dismantle the accelerator pump, clean it and reassemble it. If there is a gasket where your accelerator pump is leaking from then maybe it needs a new one. While you are there, I’d check to make sure the rubber diaphragm/pump isn’t cracked or dry or anything either. Let me know if that helps 🤙🏼

[@juzt2fresh86]

@@madjack_757 yea, I’m going to disassemble next weekend. I got the keihin rebuild kit and going to attempt to rebuild it and it comes with accelerator pump gaskets and diaphragm so planned on replacing and seeing if maybe that helps. I just gotta wait for the kit to come in it’s killing me because it’s starting to get cold and bike been bogging and cutting out so I stopped riding it last month. I fixed a couple things now that it’s down and last is to tackle the carb!

[@madjack_757]

Best of luck dude! I am in the same boat right now hahaha. Its gettin colder and I just want to ride but I'm just crazy busy :/ Lmk how it goes man and I can try and trouble shoot with ya if you need 🤘 @@juzt2fresh86

[@user-ht1dh7uu7f]

I have a custom built 43mm and someone added something to the fuel that corroded the carb it took a lot of work but I got it to run really good in the summer but even with the winter jetting it won't even start the carb and mid section didn't seem damaged in the least but the float bowl was the only thing it that the brass in the carb turns green now and I can't remove them to replace

[@madjack_757]

It might be worth picking up a new carb at this point then sadly

[@user-ht1dh7uu7f]

I'm going to try and replace the mid orings if that doesn't work then I'm done with it

[@danielcaratachea581]

Can you tell me the name of the jet that squirts the fuel into the body ? I can’t seem to find it anywhere online . Thanks

[@madjack_757]

I’m actually not sure if the physical accelerator pump jet is replaceable. It might only be able to be gotten with a whole new carb.

[@Frostbyte911]

How to tune an fcr would be great. I’m new to them

[@Leviarch244]

Just rebuilt the carb did the diaphragm and tuned the AP ran some gas through the carb off the bike and I don’t see the accelerator pump spraying any gas when I play with the throttle. Bike ran fine top end but low end it would bog. Any advice?

[@madjack_757]

Yeah I would double check that the float bowl is full firstly. If you have the carb not sitting upright, some of the gas could have drained out of the float. Secondly, make sure that you did not rebuild the diaphragm upside down. The little rubber pump has a right way and a wrong way.

[@SwormCycles]

Nice vid. I'm working on one now and even though it has had all the "YZ-F" mods done to this "WR" carb (such as the throttle stop screw mod, grey wire mod and a zip tie around the accelerator pump linkage) I still have a lean bog. Timing of spray pattern is not hitting the slide but I guess it could be too late as well? I completely rebuilt this carb including pulling the mid body with all new O-rings etc. 165 main and 48 pilot. The pump diaphragm looked OK with no visible tears but would you still replace it with a new kit or would you remove the linkage zip tie (I guess it was done instead of the O-ring mod) and re set the linkage screw to factory spec's as in your video? Getting tired of pulling this carb on/off the bike. Thanks for any pointers.

[@madjack_757]

I feel your pain on a religious level. If I were you id look into a few options. Firstly, a smart carb like a lectron carburetor is a pretty damn good performance part that can solve all your problems but it’s expensive. Other than that I would fill your float bowl and pull the slide a few times to see just where the fuel is hitting from the pump. Then make adjustments until the fuel just starts to spray as the slide goes up. Beyond that I would remove all mods and bring the carb back to stock settings or maybe even take a look into possible ignition issues, check to see the conditions of the head, how strong the spark is, etc.. best of luck to you brother 🤟🏼

[@kingshyt1980]

If the ac pump was spraying to early in to the slide would it cause a stutter in acceleration about quarter throttle … I’m having this issue after replacing my ac pump

[@madjack_757]

I hope you’re able to resolve the issue!

[@robertnelson3443]

I’ve tried all of this. Both my yz250fs 2003 bog out if you crack throttle. Could the diaphragm be bad?

[@madjack_757]

I would check the integrity of any and all rubber diaphragms. Make sure they aren’t cracked or brittle. Aside from that, perhaps rejetting could be your next plan of attack.

[@louwrensterblanche2860]

Where can i find standerd jet size for my 2008 ktm xcf w. Secondhand bike with drilled jets.

[@madjack_757]

Hey I'm so sorry for the late reply! This comment got buried in all the comments. I would check Rocky Mtn ATV/MC for parts first. Since its a 2008, you might struggle to find jets but I doubt it. My next place to look would be ebay or any other KTM parts distributors. Good luck.

[@shinobishizoku7311]

Bit of an issue with my carb off of a crf250r, when you mentioned that accelerater pump needle its not connecting inside that black arm thing where the screw is above it and when u turn thr throttle wheel that black part doesn't move at all and my carb slides are not going in all the way:/ i followed tutorial videos carefully and now i feel like i made a big problem but i hope i can fix it? any suggestions?

[@madjack_757]

Hmmm If memory serves, i am not sure if that part of the carb is modular, meaning it can be rebuilt. Is there a way you can reattach it? or will you need to get a new carb and tune that one?

[@shinobishizoku7311]

yeah it can be rebuilt, but the main issue Is that "black arm" where that screw sits in between that and that "black arm" isn't moving with it...I dont understand why that's happening, in your video it's moving with the your throttle drum but my carb isn't doing that now, does it need to be rebuilt new pieces ?

[@drey9051]

How can I reset the position of that throttle disc with the idle screw to get a baseline Idle before even beginning to adjust the AP timing ? , I turned the idle screw not knowing what I was doing.

[@madjack_757]

Hey man, I no longer have that carb but in my experience there will either be a brass screw on the side of the carb that you screw inwards to increase the idle speed or sometimes you will be able to adjust the idle in the same place you choke the carb.

[@drey9051]

Got it I’ll check that out, thank you for the advice ✌️

[@madjack_757]

Of course man 🤙🏼

[@kanishkak.bandara7048]

My Wr250F 2004 is miss firing in steady rpm . Plugs looks black colour.any ideas?

[@madjack_757]

Timing issue or maybe running way too rich

[@mattmoto441]

The jet that threads into the bowl is stick an I cannot get it out . Any secrets on getting it out?

[@madjack_757]

Heat or maybe some kinds of lubricants. If you aren’t worried about having to replace the jet you can abuse the heck out of it to get it out.

[@mattmoto441]

@madjack_757 well the blade wings are busted and it's stuck . It does blow clean so it's currently not plugged . I have another jet just dunno how to get this sucker out. If I can't I think it will just have to live in there

[@UnknownBluetoothDevice-sg1oj]

Will this be any different on a kx-f

[@madjack_757]

I’m not sure if they run FCR carbs or not but if they do then it should be the same

[@tonymckechnie9999]

Any information on the oring mod for this carb on the accelerator pump. Thanks

[@madjack_757]

Hey Tony, I've heard of the mod, but I don't think its really necessary because if your carb is tuned properly then the performance gains with the o-ring mod will be pretty marginal. Give it a try though and make a video! I would love to see the mod in action 🤙🏼

[@tonymckechnie9999]

@@madjack_757 yea I did see that the mod is just adding an o ring to the AP cam and tension screw. JD includes two types of o rings in jet kit to give you two different results. The end product is more responsive throttle off the bottom apparently. Will keep you guys posted as I have the JD kit on its way.

[@madjack_757]

Yeah it supposedly just binds the two components so they move in unison right? Yeah definitely keep me posted, I am curious to see how it turns out@@tonymckechnie9999

[@AndrewHellyer]

Hey, ive got an fcr, and its running pig rich. Changing the jetting does not seek to help. The bike starts fine, runs ok for 10 minutes then starts fouling the plug and spluttering. Has been fully cleaned and rebuilt, inckuding the mid. Any ideas?

[@madjack_757]

Yeah I would check your owners manual and just make sure that its running the same size carb that it came stock with. A previous owner could have swapped out carbs. Also, if you still have no luck, maybe look into lectron carburetors!

[@AndrewHellyer]

@@madjack_757 I think I found an issue in the cold start system. If the rubber pad on the end leaks, it's like it's running with the cold start partially on.. got a cheap Chinese one on the way to test before putting a genuine one in

[@madjack_757]

Oh is your intake manifold leaking?@@AndrewHellyer

[@AndrewHellyer]

Nah nothing seems to be leaking from the outside in, done the engine start spray thing all over, no change. It's definitely the same size carb, 39mm, although it's a KTM exc-f 6 days carb, I'm not sure if the bike is actually a 6days model, slightly different jetting to a non 6days model, not enough to make it run the way it is

[@madjack_757]

@@AndrewHellyer hmmm interesting. If you post any videos of it I’d take a look

[@stinkyholeproductions]

I have a yz250f, just had the varb rebuilt new accelerator pump Put in. It ran fins before now when i hit the gas its almlst likeit loads up. With way to much fuel and stays idled up for about 10-15 seconds before returning. Coukd thay be an accelerator pump timing issue? Any feedback is appreciated i just want to ride it and i feel like the shops trying to get one over on me and trying to get more of my money.

[@madjack_757]

Hey man, if your bike was a 2 stroke I would recommend checking for air leaks in your intake and your cylinder gaskets. But its a 4 stroke so i'd say to start by checking your air intake boot. Also did they rejet it when they rebuilt the carb?

[@stinkyholeproductions]

@@madjack_757 it's a 4 stroke and it's got the same jets it came with, I tore it down this morning and adjusted the accelerator pump. It was turned way out. I'm gonna adjust my air/fuel screw and see if that helps.

[@stinkyholeproductions]

@@madjack_757 also I noticed the rubber top piece of my hot start was not hooked on properly to the plastic nut so I put that back on too. Not sure if that had anything to do with it

[@madjack_757]

Yeah start with those. Let me kno if your solutions fix the problem or not dude!! it sounds like the shop that did the work wasn't the best 😥@@stinkyholeproductions

[@stinkyholeproductions]

@@madjack_757 I think they saw me as a "let's give em the run around and get as much as we can out of em" but hey, now I'm learning about all this stuff and from what I see they didn't know to much. The exhaust was loose when I got it back and they shouldn't of even messed with that, so that alone tells me not to bring it back. I'll keep you updated and if I can't figure it out I'll post a video on my channel if what it's doing and maybe someone can tell what's happening