sputtering at low rpm Need help

[kingriz1]

Hi I have a 93 YZ 125.

IT starts like a dream, but it wants to bog and sputter bad down low. IT seems like on a straightaway it will finally clear out and then it runsw strong till you slow down and then its all the same again.


I changed the plug (looked a little black)
Cleaned the air filter
Changed the oil
Drained the gas tank and refilled with 32:1 Mix

Ran great for a few minutes then did it again.
Any suggestions?

Thanks Riz

 

[Jimmy!]

More info would be helpful: Is this a new problem or did the bike come to you this way? Does it seem to be more related to engine speed or throttle position? Is it blubbery & lots of smoke & then clears out(this is what it sounded like to me) or is it more like there's just nothing there when the throttle is opened?

I'd go over all the basics to start: Make sure your air fiilter is in good shape and you've got fresh fuel. Make sure you've got a good spark. Then get the manual out & check your carb settings(including the float level). It helps to have a baseline from which to work. If it's a lean condition(prolly not from what you described tho), maybe pull the jets out & make sure you don't have any junk getting in the way of the fuel. make sure your float valve is working correctly & shutting off the fuel when it should(if it's not, you'll get flooding any time the engine is not using fuel as fast as it's getting to the carb). Same if it's set too high. If none of this helps, maybe have a look at the reeds as well as your crank seals.

Most any of these things could cause symptoms similar to what you've described. The more info you can provide the more accurate the feedback you get will be. ;)

 

[a454elk]

Sounds like your running too rich and it's loading up. Check to see what your jet and needle settings are along with the airscrew adjustment. Get the stock settings and go from there. It's always a good place to start especially if you don't have the stock pipe on. Not sure if you have had the bike ported or any other engine mods done but if so, it could affect it too.

 

[kingriz1]

They said that the dets were 330 and 20
Air Screw 1 3/4 out

And that the needle could not be set.

The dealership told me this. Does that sound right?

Should I replace the jets or just play with the air screw.

Sincerely,
Riz

 

[a454elk]

I don't know the specs for the 93, my kid has a 91. The pilot at 20 seems real lean and so does the main at 330. The air screw is about right but I'v never seen a needle that you can't change the clip position. It usually starts at 2nd position from the top. Pull off your slide assembly on the top of the carb and look at the needle clip, you'll know right away if it's adjustable. Then, pull off the bottom and check the main and pilot jet numbers. See what they are. You didn't say if you still have the stock pipe or any engine mods though? Good luck

 

[FLBob]

If this is a new problem, look for dirt or water in the carburetor. Take the jets out and check them for dirt (write their numbers down while you're in there).

Your needle can be adjusted up and down (I'm quite sure). Your dealer probably meant that you couldn't change the needle jet(the orifice the needle slides thru to meter the gas flow). There's a real good article on how those jets work at justkdx.dirtrider.net

 

[KawieKX125]

sounds like the plug is loadin up. try a plug with a # one lower than what you have. Then make sure the filter is not overoiled. If that does not help a leaner pilot might be in order.

 

[Jimmy!]

If you do a search for 93 YZ125 jetting on this site, I bet you'll find some good baseline info to get you started.

 

[Nevada Sixx]

i dont think mx bikes are suppossed to run clean and smooth at low speeds, especially if your trying to cruise steady at a solid quater throttle. If i get in a open field, and let my bike wind out completely at quater throttle,, mine starts spuddering..

 

[kingriz1]

I am not trying to go smooth at slow speeds. I open it wide open and it bogs.

The more I read the more I think it is loading up. I slapped a new plug in and it ran good for a couple of mins. Then the same again. I pulled the plug out and it had a lot of black build up on it. Wipes off with my finger. I am going to clean the carb and jets tonite. Put the air screw back to stock and then try it out tomorrow. I think I mixed too much oil in the gas too. I eyeballed it wrong I think. I am going to try this and then go run it for a while to see if it helps.

Thank You,

Kingriz

 

[Jimmy!]

Just any FYI: when you "guesstimate" your premix ratio, it's not helping track down the problem. Consistancy is key when dealing with jetting issues. Keep in mind that your premix ratio and oil choice will affect jetting to some degree. Also remember that changing only one thing at a time. If you change more than one thing, you can't be sure of your results.

 

[marcv125]

i would definetly check your main jet if you are wide open and it is sputtering U probably are running it to rich

 

[kingriz1]

Ok I put in a new plug then ran it for a while and checked the plug out.

It was whiteish with oil around the base. Do you think the rings could be wore out.

I cleaned the carb again and raised the needle one notch. Does not bog up high now just down low.

Runs a lot better but still bogging out wfo down low. Once it gets on the pipe it will go ok.

Thank You,

Riz

 

[Nevada Sixx]

i used to think spuddering and coughing down low could not be due to rich jetting, but when i leaned it out some,, it stopped...

 

[Racinante]

Two questions: Does it smoke a lot when you run it slow, but then the smoke disappears when you run it wide open (or close to wide open for a while)?
Does it idle? Or atleast attempt to idle?
It sounds like you might have the same problem I have with my '91 KX 250. When I leaned out my needle, it seemed to help the situation, but not totally. Messed with everything, air filter, pre-mix, jetting, compression, etc. When I pull my pipe off, and look in the crankcase, it's loaded with oil! I am getting ready to do a leak down test to check my primary compression (Compression on the bottom side of the piston) I think I have a right side crankshaft seal leaking. If I do, I wonder if someone can tell me if I can replace it without taking the engine completely apart. They way you describe your spark plug sounds like the way mine looks. Is it hard to start the first time, but every other time that day, it starts right up?

One other thing, If I ride it really fast, and keep it above half throttle most of the time, it never loads up and runs great! Loads of Power!!!

 

[kingriz1]

"One other thing, If I ride it really fast, and keep it above half throttle most of the time, it never loads up and runs great! Loads of Power!!! "


EXACTLY! I raised the needle (lowered one notch) and it ran better. Now it sputters down low but a lot less. The plug is now white not black anymore. If the jets are clogged or old will it cause this to happen. I am going to try richer jetting tonite just wanted some opinions on the jetting deal.

Thank You,

Riz