REJETTING FCR Carb | Backfire Issues

Rejetting FCR Carb due to an ongoing backfire issue. When slowing or during decel, the bike likes to backfire, more than the normal carbureted bike. I end up finding some issues that could have been avoided! This is on a 2006 YZ450F, same from 06-09.
Thanks for watching, if you enjoyed the video give it a like and please subscribe to the channel! See you in the next one!!!
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[@ericridgley3279]

How did the bike run after this video , I don’t see a update

[@DanMX2112]

Hey Eric, bike runs great and now has well over 100 hrs on it with the stock top and bottom end. Jetting is perfect and running great with no backfires. Thanks for watching!

[@cuerammer]

Use high temp silicone sealant on ALL exhaust flanges/connections, including header to head connection. Any air/oxygen able to enter the hot exhaust system will ignite any UN-burnt fuel left in the exhaust system (rich jetting), resulting in backfires, especially when decelerating! Also, when overhauling Keihin FCR carbs that are over 7-10 years old, you MUST also replace the "Mid Body" seal kit o-rings as well as the main "All Balls" seal o-rings kit! Also check the condition of you AP diaphram, and replace if needed!

[@DanMX2112]

This is great info! I haven’t replaced that mid body seal, and may be a find that is causing issues also!

[@cuerammer]

@@DanMX2112 Glad I could be of help. Please let me know if the mid body o-ring/seals kit fixes your carb issue!

[@DanMX2112]

Will do!!! 👍

[@anarchyrun8253]

I had a nightmare trying to get 07 YZ450F jetted right, kept falling on it's face during any steady throttle. After a lot of hassle, I happens to run into a old friend's family out riding in the desert. Her dad told me to unplug the TPS sensor. Apparently it is something that tends to happen on these bikes. I unplugged it, and it ran like a dream. About 40hrs later and it's still running great.

[@DanMX2112]

That’s great to know, I’m gonna try that! Thanks for the insight I really appreciate it!

[@jessecortes7250]

Would you mind explaining a bit more on what happens when you unplug it? I’m going to be rebuilding my carb on the same bike as yours and don’t want to run into any issues

[@joelsolotv7960]

I bought my 08 with the TSP switch disconnected and zip tied to the frame. When we cleaned the carb it was missing the little washer on the end of the fuel mixture screw. It solved my problems. Backfire and some hesitation when twisting the throttle. Love my bike. When it's tuned.

[@anarchyrun8253]

@@jessecortes7250 only reason to unplug it is if the throttle position sensor has failed. In my case, even with the carb cleaned and jetted right for the altitude it would stumble and fall on it's face if you tried to hold steady throttle, likely because it's getting a bad reading. Once unplugged, it cleaned up and ran great

[@anarchyrun8253]

@@joelsolotv7960 lol mine was missing that little washer too

[@joelsolotv7960]

Little washer on fuel mixture screw sometimes falls off. When I first bought my 08 YZ450F It was missing. Ran great for a 3 years now it needs a carb clean. Sad face emoji. Great video man. Very clean bike.

[@DanMX2112]

The o-ring and washer are so tiny and are easy to loose. Thanks, I work to keep the bike nice!

[@LouieGonzalezGolf]

I replaced my hot start screw too, blue anodized😎 replaced the vent lines and fuel line to blue too🤘🏽

[@LouieGonzalezGolf]

I think my fuel leak was from my fuel inlet, the 3 O-rings that go in there should be in the rebuild kit in my opinion!

[@EnduroTravelR]

Great videos man, you have way more skill than me. I'm useless at mechanics!

[@DanMX2112]

Whatever man, we all start somewhere! Apply yourself and with some KZbin help, you got this on the bag!!! Thanks for watching brother!

[@EnduroTravelR]

Daniel Tucker true, I do keep trying to get better, but making some doozies of mistakes along the way 🙈

[@LouieGonzalezGolf]

I got my carb out without pulling the shock off, bouta put it back in that way too lol my stand is just super weak...

[@michaelhealy81]

Great info. Thanks... picked up a 250 ktm 4 strk with a popping de cell and what feels like miss fire/ lag / rough pick up mid range til' high rpm. After watching this I guess I better tackle that crazy looking FCR. Arghhh. Be interesting to see what's going on. Thanks again

[@DanMX2112]

First thing is a good carb cleaning then work through jetting. Thanks for watching Michael!!!

[@michaelhealy81]

@@DanMX2112 cheers man. Yeah will do. Got a strange light drain going on too so plenty to tinker with. Could do with a shed like yours. I don't think my wife really likes bikes in her summer house : )

[@DanMX2112]

Lol the shed was fun while it lasted, but now I’m in a garage with some space finally.

[@michaelhealy81]

@@DanMX2112 even better! .... I miss living at mother's place when I need to work on stuff. Man she inherited my late Grandparents farm and out building's. Tools and space everywhere! Ha

[@davidsanseverino9612]

I have a 05 starts right up but Boggs when I hold the gas open and turns off once I stop giving gas, hit far do you screw the pilot jet and main jets in?

[@DanMX2112]

They seat all the way down in the carb body. The only adjustment on the carb is the fuel screw and idle. Everything else is adjusted internally. Sound to me like you have a main jet issue, possibly trash in the main circuit keeping the fuel from entering the carb under throttle.

[@nitro-8609]

hi daniel i have a problem when you let of throttle it popps but i had valves done to spec rebuild card had standard jetting had all air leaks fixed new intake manifold air boot i feel that my fmf s leak has a leak would that cause popping and also my slide in my card is quite loose you think you could help me thank

[@DanMX2112]

You need to make sure your jetting is good for your elevation. There are many examples online in the Yamaha forums to look at. Also, there will always be a slight amount of popping on decel, but nothing crazy, and not very time if jetting correctly. Standard jetting is good at sea level.

[@robertwoods2505]

Good job dude and sweet video. Love the bike but you need to build a garage!

[@DanMX2112]

I’m in one now finally and it’s so much better! But now I need a shop lol thanks for watching!

[@Shpan6066]

I’m not sure I’m following what you end up putting in for the pilot jet and the main jet did you go back to the 45 which is Leaner then you’re 52 right and you said you were too lean I thought so that doesn’t make sense and then the main, did you go back to the 165 and how did that all work out?

[@DanMX2112]

So I had to rewatch the video, what I found was that the lean issue was on the main jet, and my pilot was to fat, or rich. That being said, I leaned the main and the pilot to factory spec and that fixed it!

[@Shpan6066]

@@DanMX2112 ok great thank you.

[@amruth8558]

Can you please tell the possible reasons for back fire on(decelaration) a two stroke bikes

[@DanMX2112]

It could be number of things, timing, jetting, etc... normally you will have detonation issues with 2 strokes, not backfires. Start with making sure jetting is correct for your elevation and carb is clear. Along with all possible air leaks accounted for, then adjust timing to what manufacture says. Hope this helps

[@brazyss9301]

I have a crf250 my headers pipe turn cherry red & idles high plz help

[@bryce099]

I took my carb off my kx250f, same carb as this I believe. The only thing that was dirty was the throttle cable pulley and the air fuel mixture screw. I have backfires while downshifting or coasting

[@DanMX2112]

Ya sounds like the same lean issue I had. Try changing your pilot jet to a slightly larger size, and see what that does. Hope it helps.

[@bryce099]

@@DanMX2112 that's what I was thinking. I'm doing an all balls rebuild whenever it comes in and try that. Thanks!

[@DanMX2112]

Let me know what happens!

[@araxnoyfantos]

Hi, i need advice on a different issue i have with my fcr. Not the same bike, it's a xt600 with dual fcr 35, i have a strange issue when i let a little the throttle after full throttle, it makes a small bog for one second, not when i open the throttle but when i let it that's the strange. It have easy cold and warm start i can use full throttle from idle without bog but it bogs when I let it, it's a little annoying when i play with the throttle too fast. Any ideas? I have tried mj from 160 to 145 and needles from 2nt to 4th and it's still there

[@DanMX2112]

Man, I don’t even know where to start on those. That’s the dual carb with a diaphragm on one side right? I have heard those are so tricky to adjust and I wouldn’t even know what to say dude. Sorry about that. There must be some good videos on KZbin or check the moto forums online.

[@araxnoyfantos]

@@DanMX2112 thanks for replying. Yes that's right that dual it's specially for Yamaha raptor and was bolt on on that engine with stock cables. I'm using them two years now because my stock cv carb died and i'm searching for that issue without a clue. Not big issue because otherwise it runs well and i was surprised from the big difference that carb makes on the xt engine, it's night day difference, it's not works like xt and doesn't sounds ether. Man i'm in love with the carb but i need to fix this small hole that makes. Thanks again

[@Coldbrookdangee]

When you open the throttle fully you are on the main jet and it sounds like your main jet is sized right, as you release the throttle you return the main needle gradually and it sounds like your main needle is shimmed too high and is returning too fast. Buy a dynojet main needle and use the washer to shim it at 4th slot from top. Adjust it as needed but definitely will be better than your stock needle

[@sickduck66]

Stupid Question.. So My 85 Virago XV1000 With A Single Carb Using A Mikuni Hs40 Keeps Backfiring Out The Exhaust When Accelerating Low RPMs.. Ive Done Everything And Now Just Checked My Pilot Jet Size And It Was A 25.. Needs To Be Bigger?

[@DanMX2112]

No idea brother. I don’t work on the VTwins, but I would first make sure I don’t have a lean condition. Number one cause of backfires. Then work the carb. Air leak, exhaust leak, something of that nature. Sorry I’m not more help!

[@sickduck66]

@@DanMX2112 I Appreciate Your Time Brotha Thank You

[@patsavage8953]

I’ve done everything to no avail. But the silicone could be a good trick my exhaust is a little loose creating small backfire

[@DanMX2112]

That or pick up a new exhaust flange gasket!

[@Jay-vr8it]

Any update?

[@tacticalcqb]

I have a 2008 YZ450f and I recently moved back to sea level after living at 7000 ft above. I jetted it to stock specs, 160 main 45 pilot and NP-3 and she rips.

[@DanMX2112]

Nice! I’m super happy with the performance of this bike, it runs allot more linear after the jetting fix, should have a video out soon talking about that

[@seatime674]

I've got the '05 WR450F runs great but to much popping on decel is the next step to go up a size or 2 on the pilot? Thx

[@DanMX2112]

Try it and see what happens, it will always have a little bit of popping, but should be here and there, not every time. Also make sure your valves are in spec!

[@seatime674]

@@DanMX2112 Yeah it's constant popping on decel and I'm 3 full turns out on air screw I'm doing more,. I'll try a size or 2 up on the pilot see what happens. Will going up on the main also help or maybe that won't help for popping...

[@DanMX2112]

Main circuit is closed when throttle is closed, it won’t help to adjust it.

[@michaelthomas788]

Reference to the Dremel marks on your fuel injector they were trying to create turbulence over the Venturi to atomize the fuel better

[@DanMX2112]

I wondered why, but I’m not sure it’s helped much unfortunately. Have you seen this done allot?

[@michaelthomas788]

You know that the fuel in your tank is not explosive without compression so they try to vaporize the fuel so that they get a explosion because it is not the gasoline that is explosive but the vapor which is why if you've ever ported and polished ahead you do not polish the intake side you leave it rough to create turbulence like a 80 grit paper and the port on the exhaust is polished so that it doesn't have very much surface for carbon to build up on causing exhaust restriction or reverberation

[@frankiemarchese2978]

Thats crazy how on the newer gen yz gen models 06-09 you have to take the exhaust and subframe off to take the carb out. On my 01 yz426f and 05 wr450f all I have to do is take the tank and seat off

[@frankiemarchese2978]

And shock lol

[@DanMX2112]

I can and have gotten it out before without removing to subframe, but it’s extremely difficult. And even worse going back in. The extra time spent to remove subframe and shock is so worth it. My 05 YZ250F, which was a steel frame like your wr, I could have the carb off without removing anything. Thanks for watching dude!!!

[@frankiemarchese2978]

Thats awesome. I actually just re jetted me 426 carb today and I didnt even need to take the carb off the bike. I just took the float bowl 17mm bolt out as well as the front chain guard this way i can have extra room and i was able to swap both the pilot and main. It was tough feeling around for it but having a phone camera and a proper size flathead will do the trick 👍

[@paekeajiab4743]

I have a suzuki rmz 450 2007. 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????

[@DanMX2112]

Dude that’s rough, I’ve never seen an issue with smoke out the carb! Not sure about that, sounds like valve issues or something, maybe stuck open allowing exhaust back into the carb. Wish I could help but idk what to think. 🤔

[@paekeajiab4743]

@@DanMX2112 it starts very easily... If valve was stucked it will be hard to start...

[@DanMX2112]

Yes unless it was only partial open. If it ran fine before sitting I would revisit the carb. Gotta be something up on there.

[@lisameyer500]

Problem solved?

[@paekeajiab4743]

Replace or pilot jets and everything is fine now!!!!

[@bryangarcia1598]

Hey how can I fix the backfires on my 2003 yz450f

[@DanMX2112]

Start with OEM jetting settings for your elevation. All carb 4 strokes seem to have a little backfire here and there, but not every time you decel. JD jetting kits are great also, if your valves are properly adjusted.

[@snapfly7]

Do you know where I can buy a replacement accelerator pump nozzle for this carb?

[@DanMX2112]

Idk if you can? I’ll have to dig into that. I don’t think that is a serviceable part. What do you need a new nozzle?

[@snapfly7]

@@DanMX2112 I could not get mine unclogged so i took it out, it got a little mangled when removing. Thanks for looking into it

[@DanMX2112]

Bummer dude, best getting another carb from somewhere.

[@snapfly7]

@@DanMX2112 I found the aftermarket dual spray nozzles online. $100 kit, but better than buying a whole carb

[@DanMX2112]

That’s a way good deal considering a carb is around $500.

[@dannylsx]

Why is the air cut valve missing?

[@DanMX2112]

No ACV on the YZ models, only on the WR as far as I know.

[@Jjay-tw1yy]

i couldn’t get mine off without taking shock off but i didn’t try very long! i said i’m just taking the shock off!

[@DanMX2112]

Some say it can be done, but it’s so much harder in the end and more time consuming! Thanks for watching!

[@Jjay-tw1yy]

that’s what carb kit i bought and i couldn’t read the old jets numbers when i took it out so i haven’t put it back on my bike yet. should i get a 165 jet! i’m in kentucky i really hate to put the old jets back in tho because they are so corroded

[@DanMX2112]

I would that would be smart and jets are cheap so buy a kit then you can fine tune it!

[@Jjay-tw1yy]

@@DanMX2112 the jet in the all balls kit i got is a 160 guess i’ll try it i’ll order some other jets if it doesn’t run right i haven’t even been able to start the bike. i bought it not running air filter decayed fuel line from tank rotted orings on the part that goes in carb from fuel tank line wore out no muffler. i paid $300 for the bike as i said before but already have about $300 in parts in it. hopefully the engine doesn’t need any work. i’m gonna change the oil and coolant once i get it running or see how it runs

[@DanMX2112]

@@Jjay-tw1yy sound likes it needs some love lol

[@Jjay-tw1yy]

@@DanMX2112 yes it does! i’m trying to bring it back to life

[@yaseen_omar33]

Is it normal to backfire with a fmf exhaust?

[@DanMX2112]

You need to tune for an exhaust setup, especially a full system, header and pipe. You should be able to email FMF and get the correct spec for your bike. A carb bike will backfire, to an extent, but can be tuned to almost nothing.

[@yaseen_omar33]

@@DanMX2112 I have the 2006 ktm 450 xc it doesn’t have any electronics

[@yaseen_omar33]

@@DanMX2112 so should I just get the right jets

[@yaseen_omar33]

@@DanMX2112 or is it normal?

[@yaseen_omar33]

@@DanMX2112 it just back fires if I was going fast before decelerating but if I was going slow nothing happens

[@michaelthomas788]

First off it is not a carburetor if it has throttle positioning sensor and a hot start that's fuel injected for the 30 plus years I've worked on vehicles I have not seen a carburetor with a throttle position sensor other than TBI which is throttle body fuel injection

[@DanMX2112]

They have been doing the TPS on carbureted bikes for years. The DRZ models also have then. They change your fuel mapping to allow for low and high rpm compression changes and alter timing. It’s a tough thing to describe, but it’s sweet science. Now if you unplug the TPS, it essentially put the mapping into a 2 dimensional fuel map. This FCR carb is the most advanced carb before FI came about. As you can see from the video there is no fuel injection on this bike, and I think it started in 2010-11. Crazy stuff dude!

[@LouieGonzalezGolf]

About to put my carb back on my 07 yz450f, pray for me yall🙏🏽

[@LouieGonzalezGolf]

I got the same all balls rebuild kit, I’m glad I saw this so I can double check my jets! Whew

[@LouieGonzalezGolf]

Update, my rebuild kit came with the correct spec size jets but the jets in my carb were off from the previous owner.

[@patsavage8953]

It got dremelled for aspiration

[@DanMX2112]

Lol 😂

[@ThinderPlayz]

The allballs kit sucks.

[@DanMX2112]

I found it great, no issues with it at all.

[@user-hp5gx9sk2r]

.