Tips for Pilot Fuel Screw Adjustment most 4-stroke MX Bikes Kehin FCR-MX Carburetor YZ250F YZ450F

[@HorsepowerHouse20]

For anyone viewing this - ask yourself when was the last time you tore your carb apart and physically inspected all of your jets? Make sure your float level is set correctly. Also, usually the pilot jet is clogged, and often the leak jet as well. But you should go through your carb on a fairly regular basis. AND you should never use ethanol-based fuels (standard pump gas) on any dirtbike. Always use non-ethanol fuels. Also make sure your hot start mechanism (where it enters the carb) is clean and functioning properly. AND make sure the throttle pump mechanism is adjusted correctly as well. (the procedure is in your service manual.) ALSO make sure your spark plug is recent, make sure the crush gaskets relating to your exhaust system is recent as well. These are all things many people ignore or overlook on the 4-stroke motocross bikes. This is assuming your topend is recent and valves are adjusted properly. AND make sure your exhaust (muffler) packing is recent as well.

[@user-nt9vs4rw5m]

What year is that 250

[@HorsepowerHouse20]

@@user-nt9vs4rw5m 2004. Sold it for $3800 in 2019. 😀

[@FullPayGaming]

@@HorsepowerHouse20 If you get a chance, can you check out this short video and possibly let me know what my poppin may be related to. I dnt know its an airleak somewhere or maybe need to up pilot jet to a 50 from 48? kzbin.info/www/bejne/j5yof6mQrNeMkMk

[@josephmower3220]

I have a 2002 yz 250f with hot cam and crank and a weisco piston I got it on trade and I started to lose power while riding what’s wrong wit er

[@peteh8077]

But I like ethanol blended fuel. It's oxygenated pump gas. Just add a corrosion inhibitor.

[@geomi3185]

This is one of the best educational vids i have come across here on KZbin .

[@CoralReefkid]

That was helpful and you just got my bike running mint asf

[@purebloodheretic4682]

Beautiful Steel Framed YZ450 - Thats a well looked after Machine! 👌

[@HorsepowerHouse20]

250F. But close enough

[@HorsepowerHouse20]

I have several videos about this bike and many others. check out the playlist Link at the end of the video. or just scan through our channels

[@HorsepowerHouse20]

the reason it looks that way it's because it was fully restored from the Frame Up

[@purebloodheretic4682]

@@HorsepowerHouse20 Thankyou for the response - You rarely see any early era 250/400/450 5v Steel Framed YZs in such good condition! Most are completely 'Paddock Bashed' & run into the ground - They don't get enough Love! I have a low mileage '99 WR400f with YZ Cam timing Mods ect - so I can certainly appreciate what you have done to your Machine! They don't come much Cleaner than that! - I'm actually looking @ getting a legit YZ400f to restore - just waiting for the right bike & the right price to pop up! BTW Your Carby Tuning Info was helpful - I adjusted the Pilot Jet out 2½ turns & it's starting easier & not so lean 💪 I need to get the aftermarket pilot screw though - getting a Screw driver in there is a real pain in the 'A' I'll check out your other Bike related Clips - Cheers Mate! Regards Paul 🇦🇺 👍

[@HorsepowerHouse20]

I recommend the adjustable fuel screw, as well as the adjustable leak jet. look it up. it will change your life when it comes to tuning this carburetor.

[@dexteranthony2556]

Well explained Sir, Thanks!

[@gixxer7907]

My ktm 450 exc has a strange problem with the fuel screw, last time I was out I adjusted it, got it running good and very responsive then as I was riding it slowly got worse again, like hesitant to want to go at low rpm in higher gears where as when I set it, it was responsive and smooth. I can't see why it would need adjusting more than once on the same ride. It definitely didn't move, as the fuel screw was in the same place. I could understand if a big weather change but on the same ride it's just very strange to me

[@HorsepowerHouse20]

Make sure all of the tiny hardware is accounted for with the fuel screw. Washer, spring, o-ring, etc, make sure it's all there. If not, the screw will move while you are riding. Or make sure the fuel screw is not worn out. Aside from that, inspect, clean, rebuild your carburetor, and make sure all exhaust gaskets relating to the exhaust system are recent and accounted for.

[@gixxer7907]

@@HorsepowerHouse20 thanks for the reply man, appreciate it. I'll try what you said, I just know it's not the fuel screw because I only just renewed it because the o ring snapped on my old screw. Thanks again

[@HorsepowerHouse20]

Find anything yet?

[@gixxer7907]

@@HorsepowerHouse20 I don't get to ride the bike much tbh. Just gonna try adjusting the fuel screw again when I'm out, make sure it isn't moving when riding. If it still does it I'll start with seeing if it has any air leaks on the carb boots or exhaust 👍🏻

[@HorsepowerHouse20]

Did you solve it?

[@ninjazxd]

I got an 04' KTM 450 EXC that is driving me freaking insane. I won't idle for nothing, I have went through the carb like 15 times already in the past couple weeks. I have soaked the carb in carb dip, rebuilt the entire carb including the mid section. I have installed a JD Jet kit to try to get it running better. The throttle revs smoother with the JD kit but still pops like crazy after revving and the roms take a while to come back down after revs. Also it's hard to adjust because it runs super hot. Pulled back in the garage after trying to tune it and the carb is pouring gas out the overflow. I have posted that bike on Facebook for sale and I will go get a fuel injected model. Me and carburetors don't get along for nothing.

[@HorsepowerHouse20]

It has nothing to do with bikes having carburetors in general. You should either: replace your carburetor (they dont last forever,) or your pilot jet is clogged or the wrong size. Did you make sure all of your jets are the same number (size) as the stock settings? Why did you look into the carburetor so many times? Everything you are describing are lean issues. Or have you had the valves checked for proper clearance? How long has it been since that engine was rebuilt? Check the petcock inside the fuel tank (it is probably dirty.) Or check the fuel tank for dirt, or clogging inside the tank and petcock. You have a fuel flow issue, that is everything you are describing. Has nothing to do with a bike having a carburetor. Wait until you have a fuel injected bike and the fuel injection system is clogged, dirty, or has a problem. Talk about a disposable motorcycle. EFI bikes with problems or even worse to deal with. Do you really think you are going to be able to sell that bike for a good price with the issues it has? You're probably going to have to give it away. So you might as well take it to a professional to have it properly repaired.

[@HorsepowerHouse20]

Or Let a professional check it out. Instead of throwing parts at it....

[@HorsepowerHouse20]

I had a YZ250F do all of those same things, and it turned out to be nothing more than a clogged pilot jet. because ethanol based fuel does that to carburetor components.

[@ninjazxd]

@@HorsepowerHouse20 pilot jet is new, it came in the JD Jet kit. I have a petcock on order since the handle you grab is broke off but it's must be coming from Austria, says it's on backorder from KTM. Adjusted valves according to KTM service manual. Tried yesterday adjusting the pilot screw after it warmed up to get the low end idle correct and it's running so lean that it's getting hot quick. Pulled back in the driveway and shut it off the gas started pouring out the overflow. Just frustrated with that thing. I had a wr400f that gave me all kinds of carb problems and I threw an Edelbrock carb on it and it was good to go. Unfortunately they don't make Edelbrock carbs for the KTM. New kiehin carb for this rascal is $1200 and on backorder. A guy offered me $3000 for the bike last night and I put in the ad the issues it's having. I just said I wanted fuel injected because I am a diesel mechanic and everything is injected and it's familiar to me. If this guy doesn't show I may drop it off at KTM.

[@ninjazxd]

@@HorsepowerHouse20 also I went back with the jets the service manual called for for stock settings and no change.

[@carskanay]

Excellent info thanks heaps.

[@HorsepowerHouse20]

We have lots more videos of this bike and other Yamaha dirtbikes on our channel. Just search Yamaha.

[@rogerholguin5911]

Great help ,thanks alot.

[@HorsepowerHouse20]

We can help with other strange issues about this bike as well. Shoot us a question here if you have any.

[@Crayzrider_]

I have a 2004 yz250f and it’s bogging out real bad in the low rpms and after only a couple minutes of idling the exhaust right off the header starts glowing orange. Do u know anything I can do to fix it? I think ik but I wanted to hear maybe some better opinions

[@HorsepowerHouse20]

rebuild your carburetor and replace all jets. your pilot jet is clogged and can't be cleaned.

[@HorsepowerHouse20]

What did you find out?

[@dtrzay903]

What graphic kit is this?? I’ve been looking for it

[@HorsepowerHouse20]

Not available. it's from 2010.

[@dtrzay903]

@@HorsepowerHouse20 ahh. Do you happen to remember the name? Maybe I can find it on eBay. Lol

[@HorsepowerHouse20]

No one makes it. I looked for several years.

[@SASQUATCH205]

Great video, I have a bone stock 2003 YZ 450f. I have to turn the Pilot out 4.25 turns to get rid of the popping. Carb is clean. It currently has a 42 pilot. Should I go up to a 45 or 48?

[@HorsepowerHouse20]

Have you visually inspected the pilot jet and leak jet for blockage? And did you rebuild the carburetor yourself? What is the needle clip set at? Also make sure all exhaust related crush gaskets are in good condition and accounted for. There is one at the headpipe, and another where the middle of the exhaust adjoins the muffler. See your Service Manual. AND make sure your muffler packing is new. Let us know what you find...

[@HorsepowerHouse20]

If all else checks out, try a larger pilot jet.

[@HorsepowerHouse20]

What did you find out?

[@SASQUATCH205]

@@HorsepowerHouse20 raised the pilot runs great

[@SASQUATCH205]

Bike started running erratically last ride so I TOTALLY rebuilt and cleaned the carburetor. You were right, the mid-body o-rings have turned to Silly Puddy and the previous owner left the original cracked o-ring on the air/fuel screw along with a new one. I've returned to the stock 42 pilot and adjusted per your video. Bike runs great, Thanks @@HorsepowerHouse20

[@lachlanweir9847]

hey what was that black nob next to the carb thats connected to it ?? because i thought that was the adjuster screw

[@HorsepowerHouse20]

Idle screw / adjuster on the side. The other one underneath the carb is the fuel screw.

[@javiersantos8035]

Hello, my 2002 YZF 426 blows up a lot when I let off the throttle while driving, maybe I should open that screw a little?

[@HorsepowerHouse20]

you have more issues to investigate

[@javiersantos8035]

The valve adjustment is fine, perhaps it would be necessary to carburete. I meant give less fuel flow.

[@anthonyhermes3593]

When I screw mine all the way in and then loosen it a little, it becomes too loose and will turn on its own with vibrations. What could be the reason for this?

[@HorsepowerHouse20]

It's not installed correctly with the spring, washer, o-ring. Remove it and make sure all of the tiny hardware is accounted for. And once it is removed look up in there and make everything has been removed. Or it is not the correct one for your bike. Or it is old and worn-out. See your service manual.

[@anthonyhermes3593]

@@HorsepowerHouse20 You are right! It’s missing. I just ordered a new one. Thankyou!!

[@HorsepowerHouse20]

How did it go?

[@anthonyhermes3593]

@@HorsepowerHouse20 perfect! I got a new air/Fuel screw which came with a new O-ring, spring, and washer. I installed and adjusted it and now it holds in there and runs great! Thank you very much! :)

[@juancarlossantoyo3753]

Gracias 🇺🇲

[@nerwingonzalez1662]

En resumen cuántas vueltas lleva esa aguja?

[@thegodfawker5893]

Thank you!!!!!!

[@V8SRSLO1]

Is it normal on a yz450f for the first 12 inches of exh pipe to be cherry red at idle. Just bought one for my son, i have no experience with 4 stroke

[@HorsepowerHouse20]

Yes. Because they have titanium header pipes, they get red when hot. And don't let any 4-stroke sit idling for long. They will overheat.

[@strubies]

Do they all have that screw? How do you adjust if not?

[@HorsepowerHouse20]

It is very difficult to access. I recommend you install an aftermarket one as shown.

[@leon2k079]

I bought a Yamaha yz450f 2004 and I noticed that my bike was always popping out of the exhaust, then I wanted to look at the carburetor and I noticed that I don't have this screw to adjust. I only have the idle speed what should I do?

[@HorsepowerHouse20]

The fuel screw might be hiding up in there. Look under the carb up in that area (where you see mine). the original screw is very small. you need a very small screwdriver to adjust it. I highly recommend you buy one like I have in the video. You can get them at any online dirtbike parts store (it's called an Adjustable Fuel Screw.) But if the carburetor has never been disassembled and cleaned, I recommend you do it. And remove all jets and inspect them for blockage. The pilot jet is probably clogged. Make sure you remove the pilot jet and LOOK THROUGH its tiny hole. the pilot jet is difficult to clean because it is so small. you will see what I mean. it is usually best to just replace it. Buy a carburetor rebuild kit as well. You'll be glad you did. Let us know what you find out. -BikerDave

[@leon2k079]

@@HorsepowerHouse20 Thank you very much for your help I will check if everything is ok there. I have another question, where did you get your radiator thermostat from? Because I don't trust the eBay China thermostats to stay tight. It would be great if you could send me a link you bought yours from.

[@HorsepowerHouse20]

they are all made in China. just like 95% of everything we buy in 2023.

[@HorsepowerHouse20]

Did you solve it? Do tell.

[@oliverkoler7224]

where can i buy this adjustment screw?

[@HorsepowerHouse20]

Any dirtbike accessory online supply store. google.....

[@MrCallyone]

Got an yz426 my dad finished building and I was wonder why I was having crank over issues I believe he had it set too lean, cause first kick it made a pop and then a couple kicks later it wanted to turn over but it died off

[@HorsepowerHouse20]

Too lean. install a larger pilot jet or make sure it is not clogged.

[@HorsepowerHouse20]

Did you get it resolved? what was needed?

[@cuongly523]

Does outside temperature matter when tuning? It’s about 40 outside. Should I wait until it’s gets nearer 60+?

[@HorsepowerHouse20]

No

[@HorsepowerHouse20]

However if you rarely ride in cold conditions you might as well not change your jetting. Tune the carb for the weather you typically ride in.

[@EXTREMENESSBMXMOTOCROSS223]

I have a weird issue going on I have that exact same carb it'll fire first kick idle and rev and doesn't bog but when I turn the choke on it won't raise the idle and sometimes kill it my other issue is when I put it into gear the idle will rise those issues aside the bike rides amazing and has insane power if anyone can help me out that would be appreciated I checked for air leaks and I can't find one I installed the spring washer and o ring on my air fuel screw put it back together and fired first kick air fuel set correctly and still the choke doesn't raise the idle and the idle will raise when put into gear although after the rest of the pieces on the air/fuel it made the issues a bit better I was able to adjust it out a little bit but it's still doing it, I wonder if I could possibly have an air leak but when the bike is in neutral it runs normal

[@HorsepowerHouse20]

if a 250F has "insane" power, it is definitely running lean or something else is wrong. Those bikes are not insane. A 450, maybe, but not a 250F.

[@niconine268]

Bike is mint & jacked

[@HorsepowerHouse20]

All of my bikes are. 👍

[@step0807]

Hi, I have a yz250f 2005. Cleaned the carb completely, checked all the jets, checked valve clearances, everything should be fine. I got the bike running fine, I just have troubles with starting it. I adjust fuel screw that it starts on second cranking with hot start activated. Then I try it again half day later, and it again needs mora cranking or adjusting the fuel screw again. And I am always walking between one and a half turns out and 2 turns out. It just behaves different every time. Any tips please?

[@HorsepowerHouse20]

a 4-stroke has issues starting if low circuit (pilot) carburetor settings are lean. Install a richer pilot jet. Richer needle clip setting might be required as well. And make sure you visually inspect your current pilot jet and/or leak jet for blockage.

[@step0807]

@@HorsepowerHouse20 I will try it and give a feedback for others. Thank you!

[@HorsepowerHouse20]

What's the latest?

[@step0807]

I still did not catch time to deal with it. Maybe in upcoming weekends. I will get back.

[@HorsepowerHouse20]

any udates?

[@BEAMERNOOB]

mine is lose and turns out of adjustment when its running. is there a o ring that is supposed to hold it in place?

[@HorsepowerHouse20]

Yes. And a tiny spring and washer. Buy a replacement fuel screw kit. Get it pretty much anywhere motorcycle parts are sold.

[@HorsepowerHouse20]

Did you solve it?

[@goatyachty1762]

I have a 2005 yz250f and I have a hard time finding a new frame guard for it. Do you know anywhere that might sell them I want a very basic simple looking one. I also see how they don't make restyle kits for them only the two strokes. I want to put a newer looking front fender on mine. I might get like a newer year fender and just re drill new holes

[@HorsepowerHouse20]

Drilling the fender is easy. I do it all the time. You Googled "Frame Guard" for this bike and found nothing? They are still made. I have more videos and a photo album of this bike.

[@HorsepowerHouse20]

My 2004 Yamaha YZ250F Atlanta GA: kzbin.info/aero/PLVsdJzatTm_XQENhyh_7VWo0uWaGwg18D

[@Aidans_Mx]

Hey man I know this is an older video but I have a 01 yz250f just replaced top end gaskets and seals and rebuilt carburetor, the bike won’t start up on choke or without, only starts with hot start, valves are in spec no smoke and good compression and revs out fine, if you push in the hot start and rev it the bike bogs out and dies, any idea what this could be I’m leaning twords jetting, and i think it’s running rich because it’s running good with the hot start witch leans it out and fuel screw was at 1 3/4 any suggestions?

[@HorsepowerHouse20]

Did it run fine before you worked on the bike? When is the last time you thoroughly went through the carburetor and all jets inspected for blockage? And who did the top-end job? Might want to double-check their work...

[@Aidans_Mx]

@@HorsepowerHouse20 thanks for the fast reply, I did the top end, and I just fully rebuilt and double checked the carburetor

[@HorsepowerHouse20]

Double-check your work - especially if it ran fine before you touched it. A bike doesn't stop acting right for no reason...

[@HorsepowerHouse20]

On 4-stroke dirtbikes and cars, bogging usually means LEAN or clogged Pilot Jet, Leak Jet, or incorrect float level in the carb. They will also be difficult to start up when lean. They will still run when rich, but you will see black smoke out the exhaust when revving it up. Make sure you physically look through the jets. Don't assume just because you blew some carb cleaner or air through them that they are clear of blockage. A few years ago a clogged pilot just stumped me for 3 weeks. Bike ran like shyt. That's all it was.

[@theanimechannel961]

I have a 2004 yz450f the bike has a high compression piston r&d power bowl 2 stainless steel wise cove valves and springs new car boots and clamp exhaust gasket is brand new wiseco clutch basket with wise gold clutch springs and clutch pack the bike is sluggish for a 450 if I twist the throttle in first the bike comes up but if I'm in second the bike doesn't have enough power to come up I'm 195 to 200 lb also have a JD jetting kit that idle hangs and it just doesn't have good power I know it's running lean cuz it pops the valves are shim suspect check the multiple times the timing is perfect I'm clueless

[@HorsepowerHouse20]

Post a video of the bike running. And of you riding it.

[@HorsepowerHouse20]

Why do all of that to the bike? All of those "mods" etc? Or did the previous owner do all that? And how long has it been since it was rebuilt?

[@HorsepowerHouse20]

Here was my 2004 YZ250F. El Perfecto. ;) kzbin.info/www/bejne/eZW2oomqnqiEa7M

[@HorsepowerHouse20]

Oh another thing I DON'T Recommend on these 4-strokes ---- a fuel filter. They rob the carb of fuel flow - causing lean issues. I used to use one - not anymore.

[@HorsepowerHouse20]

Did you solve it?

[@Ebbrush3]

my clog was in the mid body

[@TheWhole36]

My bike doesn’t start with the choke on will start and run fine with it off but if I turn it on it kills the bike can you help

[@TheWhole36]

And a bog in neutral if I full throttle

[@HorsepowerHouse20]

Rebuild the carburetor. check all jets for blockage. pilot jet is likely clogged.

[@HorsepowerHouse20]

Post a good video of it running, idling, riding, etc.

[@HorsepowerHouse20]

What was the last thing you did to it when it started doing this?

[@TheWhole36]

@@HorsepowerHouse20 just bought the bike, when I first bought it it was hard starting I reshimmed the bike now it runs n starts like a dream but chokes never worked since I’ve had it and just kills the bike, I will get some vids of the crf this weekend Thanks for your help

[@jameslawson7248]

I have an issue with my ktm 250 sxf 2006, when decelerating it pops extremely loud almost like a firework or gunshot…. I’ve tried a bigger pilot and adjusting the fuel mixture. Could you help me on what to do?

[@HorsepowerHouse20]

How many hours on it? When was last top-end job, valve adjustment, carburetor service, fuel petcock strainer service, etc etc etc.....

[@jameslawson7248]

@@HorsepowerHouse20 well I bought it off my neighbor in February and he said about a year ago a fresh top end was put onto it, then it sat in a shipping container for a few years. When I got it I took it apart and sprayed it pretty well and it ran really good. Only problem I had with it was the cold. That thing would not start in any weather below 40 degrees. But other then that it runs like brand new. Just back fires a lot and can’t seem to find the issue

[@HorsepowerHouse20]

@@jameslawson7248 I would let a pro mechanic handle it. You will spend weeks / months and random parts thrown at it and still maybe not resolve it. Just being real with you. These bikes are not simple and very finicky when a running issue arises. (And I have been working on bikes for 25+ years) The list will be long of the POSSIBILITIES you need to investigate. Just No.

[@HorsepowerHouse20]

If nothing you have done affected anything - you are investigating the wrong thing. Let a pro mechanic handle it.

[@HorsepowerHouse20]

What did you figure out?

[@racingdreamz8021]

I tried on mine but I couldn’t get the popping to stop at all

[@HorsepowerHouse20]

That means it isn't your issue.

[@racingdreamz8021]

@@nalyd6386 Will do, Thank you

[@nalyd6386]

@@racingdreamz8021 I’m having problems aswell with my 2008 (carbureted) crf250r. I’ve checked for air leaks, can’t find any, I’ve upped my pilot jet, still has a hanging idle, to me, this is abnormal. I will let you know if I find the culprit.. at least hope to remember.

[@racingdreamz8021]

@@nalyd6386 Try blowing air through your carb with an air compressor, Right through the gas line

[@racingdreamz8021]

@@nalyd6386 any luck?

[@allanknight1910]

Looks like your o ring has popped down on your mixture screw

[@HorsepowerHouse20]

No.

[@HorsepowerHouse20]

I put an extra o-ring there on purpose - to keep dirt and crap out of that chamber.

[@DM56fmx]

Just wondering if your carb is completely stock settings?

[@HorsepowerHouse20]

Close enough. If your bike will not run on stock settings - unless you live at an extreme altitude - you have other problems to investigate.

[@Oxaqx]

how to i figure out the factory jet setting for a bike that has been messed with before i owned it

[@HorsepowerHouse20]

Same as with any carburetor- remove all jets and compare to factory settings.

[@DynastyJr]

Mine isn’t idling

[@snowrider4495]

Start with cleaning out the carb and jets. Mine would only idle with the choke on until I cleaned out the carb from sitting a couple years.

[@HorsepowerHouse20]

Remove the pilot jet and look through it. it is probably clogged. Just replace it. That is if your entire carb has never been thoroughly cleaned or rebuilt...

[@snowrider4495]

@@petver5259 I did and that was the case. Too small main jet I have bad eyes without glasses so I had a 130 instead of a 180 main jet. I also increased the pilot jet and it's running well now.

[@HorsepowerHouse20]

I've had more than a few pilot jets that could not be cleared out. Crusty ethanol fuel will do that.

[@DynastyJr]

@@HorsepowerHouse20 i have a question. Recently my dirt has started bogging down after idling with the choke out. It idles while it’s cold but as soon as it gets warm and i let the choke back in it starts to die and turns off. Is likely just the carburetor?