hello I have a 2009 yamaha xt250. I recently put a fmf powercore 4 slip on muffler, and a #140 main jet. now I basicaly have 3/4 throttle and up anything bellow it spits and sputters above 3000 rpm. Im tired of having this issue, I have tried the stock jetting, cleaning the air filter and putting the air box lid back on and the issue still presists. Anyone have this issue?

Any input is apprecatied.

I have a 2009 xt250 with the fmf and a #140 main jet too,    i have no issues,


what is your issue exactly?  im not fully understanding what you described.

And you cant really clean that paper filter,  they get really clogged up quick,  gotta replace it,  or cut out the paper and stick some UNI air filter material in there,  since there is no aftermarket air filter for this bike.

Have you done the air/fuel screw 3 turns out mod?

150ron, on 04 July 2012 - 10:17 AM, said:

I have done the 3 turn mod, although im closer to 2 turns.

Ill try to explain. the problem happnes all the time but its the worst on the highway. When im at about 50-65 mph (5000-6500 rpm) I can eaisly run at under half throttle, but if I let off it will pop and sputter and I have to move back to half throttle to smooth it out. When this happnes its almost like its running out of gas.
I tried running with no air filter and it was doing the same thing so I dont think thats the issue.

Sorry if I sound pissed, im just tired of having issues with my new bike.

Sounds like it is lean on part throttle.  Have you tried shimming the needle in the carb with a small washer (or 2)?

You would think that putting the airbox lid back would help, but I don't know these bikes that well- maybe the airbox isn't really a bottleneck?

Basic troubleshooting would be to reverse the changes you made to see if it goes back to normal.  Personally, I don't getting pissed at the bike is the right response.  It didn't put those aftermarket parts on.

pj5454302, on 05 July 2012 - 03:33 AM, said:

Hmm,  you might have something else going on,   for the pop and sputter when letting off the throttle,  i think that means that you need to go up on your pilot jet,   or turn the air/fuel screw out to 3 full turns out,  that way its still getting enough fuel.


Also does not sound right that you are able to go 65mph with only half throttle,  my bike definately needs more then half to go 65,  not wot,  but more then half.

I did add a small shim to my jet needle,  since our needles are not adjustable  you have to find a small shim and put it under the stock white shim that is allready on the bike,  that way it raises up the needle a bit and gives the engine more fuel,  this mod has worked well for me and produced pretty good power.

do you have a fuel filter on the bike,  maybe check that.


maybe your carb jets are dirty or partially clogged,  a good teardown of the carb and cleaning might be in order.

how many miles on the bike?


i recently tried to modify a stock air filter,  since there is NO aftermarket air fitlers for our bikes,  so i cut out the paper and glued in 2 layers of UNI air filter material,  bike ran great till about 3/4 throttle,  then from 3/4 to wot it stumbled big time,  so i put the stock air filter back in and it now runs better then new,   i do not know if its getting too much air or not enough with my modified filter,  will have to play with it and either add material or remove some,  see if i can get this figured out.


you might need to clean your carb,  or if you dont want to do that just yet,  go get some seafoam,  and some fresh gas,  put it in the tank,  with a good amount of seafoam and go ride the bike for a hundered miles or more,  see if it becomes better.


I can imagine you are fraustrated,  dont worry we weill get you sorted out,

also check out xt225. com,  theres a lot more info on that site for our bikes then on here,  many over there have a lot of experience,  more them me anyways.

Edited by 150ron, 05 July 2012 - 01:12 PM.

I put it all back to stock when it first started acting up and it had no effect. Ive Had the carb apart about 4 times and everything seemed clean.
Bought the bike with 750 miles, it now has just over 3000. Oh and at an indicated 65 I can maintain speed at just under half throttle, well i used to be able to before this problem. Oh and shimming the needle makes its waaaaaayyyyyy worse

Edited by pj5454302, 05 July 2012 - 02:41 PM.

Man,  i dont know..  im sorta new to motorcycles myself,  so have very little experience.

try posting this issue on xt225 and others will chime in.


So you think the problem is that they bike is starving for fuel?

Im thinking your issue maybe something else, if the carb is clean,  and youve tried running without a air filter.

150ron, on 05 July 2012 - 02:48 PM, said:

Thats what what im thinking, but not sure.
thanks for your help, and I have tried joining multiple times but it never lets me.

Edited by pj5454302, 05 July 2012 - 02:59 PM.

I'm new to them as well, so my opinion isn't worth much.  Maybe check from the peecock to the carb.  Take it off and see if you can blow through it.  Maybe you've got some crap in your lines.  Sounds like it's starved for fuel.

Yeah,  i was kind of thinking that too,  that maybe its just a simple problem somewhere,  also remove the fuel line from the carb and let the gas drain into a bowl or something,  and see that gas comes out nice and steady,  in the reserve position too.

as fat as xt225,   you need to first register and post a line in the introduce yourself section i think,  and it takes like a day or 2 and then you are good to go.   i have a feeling over there you will get sorted out.

have you tried a new spark plug?    im thinking it might also be electrical maybe,  since you went back to stock setting to check and it still had that stumble.

try doing all the little things first,   check gas lines,  new spark plug, change oil, check valve clearance,  new air filter,  remove both pilot and main jet and shoot wd-40 through them,  make sure they are perfectly clear,  check your float height level in the carb.

well took everything apart and cleaned it. .The whole carb and the peecock. .And no change, so Ill try a new spark plug one of these days

If youve put everything back to standard and it still does it, it points me towards youve disturbed something when you first fitted the add on's. As someone else on here has said then run the same modes with no issue's(ok not sure on altitude difference which plays a factor for you state side guys). Perhaps youve damaged/knocked the float/level or loosened some swarf in the carb/intake system as it does sound air/fuel related as opposed to electrical. When putting the tank back on is the fuel line straight/free flowing. Just check plug condition to start with, nice light brown tip.

Good luck, can be annoying but at the same time helps you learn about the bike...........thankfully over the years ive moved away from the 'if in doubt give it a clout' approach and now think things through....usually lol

Well went on a 250 mile road trip and I have pretty much pinpointed the symptoms. .I basically have no 1/4 throttle, Thats where the sputtering is no matter what rpm. Not sure if that helps with a diagnosis but thought id post it. oh and the fuel line is straight and I hear what your saying but everything looks correct in there and I was always careful with the carb and other parts. But that being said Ill check the plug today and see what it looks like.

Edited by pj5454302, 09 July 2012 - 04:10 AM.

replaced the plug and it was a solid black. Still dealing with the same f@$%ing problem.

have you checked your carb boots? made sure neither are torn cracked or loose or anything? you could have the filter side of the carb almost out of the boot. it happens alot. i usually put the back on and tighten it down first and then go to the motor side of the carb.

checked the boots and they are in tack. I loosend both up and re sungged them. No change

Sounds simular to this

http://www.thumperta...running-issues/

but I dont want to spend $260 on a new carb and still be having this issue.

Do you have a seat cover of any sort?  I put on the Coleman ATV seat cover and as soon as i did that, when I got to 3/4 throttle, it would begin sputtering which prevented me from going >60 mph.  After a couple of days of doing this I noticed that the straps to hold the seat cover on, were getting sucked up by the air box snorkel restricting the airflow. Once I trimmed the straps and made it where they could not get sucked up, she started behaving again.  

Have you verified that there is free air flow in the air box?

Black plug is too rich. White too lean. If you're running rich at 1/4 throttle, could the float level be off? If it is too high, at low throttle openings, there will be an excess of fuel.
The air screw/mixture screw/pilot jet controls idle to about 1/4, then the cutaway on the slide takes over from about 1/4 to about 5/16, then the needle/needle jet, from there up to around 3/4. From 3/4 to WOT, the main controls everything. You start at main jet, then get needle/needle jet, then pilot. Put anti seize on plug threads and avoid removing while hot or you're going to pull the threads one of these times. There is of course overlap for each circuit. Be sure no diaphragms are ripped on your carb. I believe it has a closed throttle enriching circuit, so it won't pop while you go downhill with the throttle closed. If that is messed up, it will beat you to death.

If I were having problems at 1/4 throttle, first up would be verify float level, and be sure it isn't sticking and slightly overflowing. Then fiddle with air screw until it started to blubber, then back off until clean, then one quarter turn more in that direction after I though I was satisfied.

The air/mixture screws are of two types: if at the engine end of the carb, they control the amount of already mixed fuel and air around the throttle plate. Older pre-FI cars were like this. You back them out, they get rich, you turn them in, they get lean. You warm up the engine, then carefully in one quarter turn increments turn it out until it start to stumble, then crank it back in until clean, then one quarter more. in colder weather, you'll have ti turn it back out again, and warmer, back in. (I don't miss carbs a bit)

If the screw is at the air filter end, then cranking it out allows more air to mix with the pilot/idle jet fuel and makes it leaner, turning it in makes it richer.

My guess is yours is at the engine end, so ccw= rich, cw= lean.

if you had a two stroke, you  make it as rich as it will run, then slightly lean. Four strokes, you make them as lean as they will run, or you end up with excess fuel diluting the oil on the cylinder walls and causing rapid ring/piston wear. You can tell a rich four stroke as the oil has a fuel scent to it. Not great for engine longevity.

Try this and let us know, it isn't rocket science. You don't need a new carb, it is fixable. Throwing parts at it isn't the answer if you're not aware how it works. Do one thing, evaluate, do another evaluate, etc. Multiple changes lead to inserting more problems than you fix.

BTW: Don't run without air filters. If it were the filter, it wouldn't need the choke and would gag all the time.

Again: I don't miss carbs at all.

Edited by Yamaguy55, 01 September 2012 - 06:03 PM.

pj5454302, on 04 August 2012 - 01:56 PM, said:

The older XT350 had TK carbs, so you might be able to find suitable jets from that model and the TT350. Look at the Yamaha parts lists, they say what size the jets are.