Hi guys,
i currently own a 09 yz250f with athena 290.
The problem is when i ride at steady rpms(which can be as 1/4 or even 1/2 or even 3/4 throttle opened) the bike is not possible to ride. It's so annoying... As if someone gives and takes away my throttle every second. If i twist the throttle the bike responds amazingly, no bog, no hesitation of any kind. When riding in the woods is not a problem but when on fire roads - arghhh. I have taken off the carb but didn't check it, clean it or see what the jets are. Another thing is that it is impossible to start it cold if i dont pull the hot start. Choke on - no chance, choke off - again no chance. Pull the hot start it fires from 1-2 kicks. Also when hot i have to pull the hot start and it fires from 1-2 kicks.
I will take the carb off, clean it and see what jetting it's in. I want to see if there is a rubber on the easy access fuel screw(PO may have not put it). But it will be nice if you can give me some advice what procedures i can do before taking it off for determining rich/lean or which jet to check or riding with choke on/off, hot start and so on... I have tried unplugging TPS but bike lost a lot of power but as far as i remember that sputter went away. I did follow the manual and troubleshooting the TPS and everything was in spec....
P.S. i know that there are a number of topics about jetting but my problem is strange for me because i cant start it normally. Valves in spec.
Thanks! (otherwise it's an amazing enduro bike! Keep that in mind!)

Edited by nk_dimitrov, 28 April 2012 - 10:21 AM.

The yz race bikes aren't made to go at a steady 1/4-1/2 throttle. They are made to be wide open and then on the brakes. I think you'll find it very difficult to have no bog/hesitation  at full throttle and also no bog or hesitation on steady 1/4-1/2 throttle. You may need to comprimise and see bog/hesitation on both but not alot or stick with what you got.Your lucky, i know alot of people who cant even ride full throttle and just open it up without bog or hesitation! Especially with a 290 kit.

Edited by 08rider, 28 April 2012 - 11:11 AM.

I disagree with 08Rider, there's definetely something not right with your bike. There's no way that the problem your experiencing is something normal, or something you should have to "stick with". Your bog\hesitation most likely the result of improper jeting, or somethings wrong with the carb. Definetely continue with taking the carb off, cleaning it and tearing it apart for inspection. The guys on here will be able to help you figure it out.

What mods have you done to your bike? Have you done the O ring mod? Jet kit? Etc?

The carb has easy access fuel mixture screw, BUD racing acc pump cover and O-ring mode. I dont know if there is a Jet kit inside. I just checked to see if the pilot is clean before assembling the bike. This is the strange thing - hard to start but when running there are no bogs or anything BUT when i have to ride like 5miles on road or open fire roads it's impossible...( it doesn't matter if i ride with 10, 20 or 50km/h because if the throttle is fixed it's cutting very very badly...) It's little bit frustrating reading like you bike fires from the 1st kick when hot or cold and i have to kick it with hot,choke,throttle etc etc to manage to start it somehow... Just want to know what can i do before taking the carb off - where to look for the problem. Cheers!

Edited by nk_dimitrov, 28 April 2012 - 03:00 PM.

You need to remove the carb. The way you are explaining it it sounds like your needle  is too low. Try moving the clip down one groove to richin the mid throttle part of the carb circuit. It doesnt require removing the carb to do but it would be a good idea to clean it out good.

A clean carb is a happy carb.

If you need the hot start to start it cold then it sounds like you are very rich. Pull you're idle mixture screw and make sure that little tip is still on there and straight also make sure all jets are in place and not sitting in the bottom of your float bowl.

Definitely sounds too rich on the pilot circuit for starters.  When you roll on the throttle slowly from 1/4 to 3/4 is it smooth, does it hesitate, or jump to life suddenly?

What is your elevation above sea level? And can you get us your current carb specs (pilot jet#, main jet #, clip position on needle)

I ride at about 1000m = 3300 feet and now it's around 22-23 degrees = 73 F . If i do anything with the throttle there is no problem. I can twist it as fast as i can from idle to WO and the bike spins faster than i can react. There is not even 0.001 second delay(figuratively speaking) or bog. If i hold it at one place it starts cutting off... Ok guys, thanks. I don't want to waste your time guessing before i take it off and see what jetting i have. When i do i will write it here to see what we can do about it. I like how the bike reacts so i am hoping that it has to be cleaned or some jet has loosen inside. Cheers!

Edited by nk_dimitrov, 29 April 2012 - 02:21 AM.

intensem1rider, on 29 April 2012 - 02:05 AM, said:

+1 on being too rich. When going to a big bore kit your jetting will need to be adjusted much leaner.

At that elevation I would start with a 40 Pilot and 165 main and go from there.

Definitely Jetting related, start by getting your pilot dialed in according to directions in manual once the bike is at operating temperature (40 does sound like a good place to start but you may find you need to be a bit richer). Big bore kits often require a needle change too in order to get them smoother in the mid range, lastly, wide open...see if it pulls stong and even or falls on it's face and adjust accordingly.

I'm going out on a huge limb here bit you might want to check your cam timing. A few years ago I rebuilt a old xr and ended up putting the cam in upside down. Surprisingly it ran and it revved up pretty good but it would have a weird cycle particularly at higher rpms excactly like the OP was talking about. Is it possible you got the E and I mixed up on the cam? I get that the 2 bikes being compared are very different but they're both 4 strokes so it is possible.

Hi guys,
i've been very busy lately so i finally got a chance to take the carb off. So what was in there:
Needle: NFLR 3rd position from top
Main:185
"JET, SLOW": 45
Jet(AP): 72
I ride at about 5000-7500ft and now it's 80F

So the carb seems clean inside, i will disassemble everything and clean it. But what do you think about the jetting and is the needle the problem of my steady throttle sputtering or is it something else? Thanks!

Edited by nk_dimitrov, 07 June 2012 - 07:09 AM.

nk_dimitrov, on 07 June 2012 - 07:09 AM, said:

IMO, you're waayyyyy rich.  Do what intense1 suggests on the jetting and test. Be warned that this may (or may not) create a bog but that's easy to tune out with a richer leak jet.  Just roll the throttle on instead  of a quick twist.  I think you'll need to lean the needle as well.  If you think it runs great now, wait until you get the jetting spot on.

I ride around 4200 all the time.  Riding a bone stock 06 250f.  Stock slow jet is a 45 I believe,  went to a 48 and it helped bike out alot.  Also double check the air fuel mixture screw at that elevation there is less air so you might have to play with it a little.

So i may try a 40/42 pilot and i see that a lot of 290's use 170 main. I can try 2nd position. But as i read on in the forum i see that my needle is not used by anyone. So can you suggest a needle too? P.S. JD has to be imported and it gets really expensive... Thanks!

Edit: I did some more reading and the NFLR was the stock for 05-06 or something like that. But that doesnt matter because there are plenty of riders that are happy with it for the summer so i am sticking with it for now. When jetting arrives i will post results. Thanks!

Edited by nk_dimitrov, 08 June 2012 - 08:28 AM.