05 YZ250 Throttle Response - No roll-on


49 replies to this topic
  • digitalkidd

Posted September 22, 2007 - 03:53 PM

#1

I don't know the best way to describe what's happening, but I hope this makes sense for someone to help.

Because 1st and 2nd gear are so short - I'll reference third.

WHen I roll on the throttle, I can hear it sputtering through the range, but when it gets to the power band, it takes off as it should.

It seems my only smooth throttle response comes only when it hits the power band regardless of the gear i"m in....especially 1st gear.

I haven't touched the jetting and I'm using Motul 800 40:1..I have a fresh air filter, but something just isn't right.

Oh yea...I have the throttle adjustment all the way in.

I think it could be one of the following:

throttle cable
spark plug
jetting
bad mixture
throttle tube??

I don't know what to do...I'm going to kill myself at the track.

Any help would be appreciated.

  • rm125ridwe

Posted September 22, 2007 - 04:03 PM

#2

sounds like a power valve problem

  • BRM

Posted September 22, 2007 - 04:15 PM

#3

Possibly Jetting, sounds like its spluttering before getting into the power band. I would suggest you drop the needle a clip and/or drop the pilot jet to a 48.

  • digitalkidd

Posted September 22, 2007 - 06:07 PM

#4

How do I drop the clip? I'll look for it in the manual...I've never messed with the jetting before.

I hope it's not a valve.

Thanks

  • dino 702

Posted September 22, 2007 - 08:54 PM

#5

Not knowing your alt. or temp. I would concure on the 48 pilot. Once I droped mine from a 50 to a 48 it was like a whloe new bike from the roll on to mid.

  • hallsy

Posted September 23, 2007 - 06:02 AM

#6

I'd agree with jetting, our 03' sputtered from just above idle to @ 3/8 throttle opening, from there it would run fine. You should check your carb. to see what needle, clip position, float hieght, and jets(main, pilot), are in there. With that, your elevation, and maybe your riding conditions you will get alot of good info. from the folks around here. Your bike came stock with a 178 main, 50 pilot, needle N3EJ set at clip position #2(second groove from the top). Note: BRM recommended dropping the needle not the clip, to drop or lower the needle you have to raise the clip 1 notch, if you do that HOLD ON cause that baby may run like a scalded ape!

  • mxjosh

Posted September 23, 2007 - 09:08 PM

#7

Have you ever cleaned the powervalve since you have had it? I had some screws back out so it wasn't closing. Bottom end was non existent then it would hit hard from mid on up. Very hard to ride and no matter what jetting you do it will never fix it. I would check it.

  • digitalkidd

Posted September 24, 2007 - 06:28 AM

#8

I'm not completely incompetent, maybe partially, but I don't know how to access the carb to make the clip/needle adjustment, or how to access the powervalve and what to check/adjust.

Based on the suggestions, I want to start by checking the power valve and then move on to the jetting.

  • rusky

Posted September 24, 2007 - 06:37 AM

#9

yea its wouldnt hurt to check the powervalve, if its sticking then whatever jetting changes you will make wont even make a difference.

The powervalve cover is right above the exhaust port.

To change needle position first you need to take the carb off the bike. Then look at the two screws the screw the slide in place (where the throttle cable goes). Take those screws out and the slide should just come out, there will also be a TPS lever but dont worry, the slide assembly should just slide out. Once the slide is out you have to pull back the spring and then compress the throttle cable to take it out of the slide. Before you do that there might be a small plastic piece inside the slide, you have to take it out. Once the cable is off the needle should just slide out.

Anybody feel free to correct me, I havent change my needle in a while so i dont remember exactly how all the pieces fit in there.

  • Denn10

Posted September 24, 2007 - 08:03 AM

#10

I think you need to get someone to help you out to see exactly what jetting you have in it now if your not sure how to pull it all apart. Is this a recent thing that just started happening or always been like this?

  • Loaner

Posted September 24, 2007 - 10:12 AM

#11

I'm not completely incompetent, maybe partially, but I don't know how to access the carb to make the clip/needle adjustment, or how to access the powervalve and what to check/adjust.

Based on the suggestions, I want to start by checking the power valve and then move on to the jetting.


Easy place to start

pull the power valve linkage cover of on the exhaust side of the bike. Right above the water pump(it has the only un exposed cyclinder jug bolt in there). After the cover is off, start the bike. If the linkage is moving up and down when you crank the throttle, then it's probably not the powervalve.

When was the last time it ran clean. What have you changed since then?

  • mxjosh

Posted September 24, 2007 - 11:22 AM

#12

yea its wouldnt hurt to check the powervalve, if its sticking then whatever jetting changes you will make wont even make a difference.

The powervalve cover is right above the exhaust port.

To change needle position first you need to take the carb off the bike. Then look at the two screws the screw the slide in place (where the throttle cable goes). Take those screws out and the slide should just come out, there will also be a TPS lever but dont worry, the slide assembly should just slide out. Once the slide is out you have to pull back the spring and then compress the throttle cable to take it out of the slide. Before you do that there might be a small plastic piece inside the slide, you have to take it out. Once the cable is off the needle should just slide out.

Anybody feel free to correct me, I havent change my needle in a while so i dont remember exactly how all the pieces fit in there.


In addition to that, the needle will not slide out after you have pulled the cable and spring out. The cable is hooked in but just push the cable down and move it away from the center and it will unhook. I usually release the pressure off the cable by taking it out of the throttle tube.

After the cable is out, you will need a 6mm socket to unscrew the cap that holds the needle in place. The needle will now slide out. Remember, moving the clip up will drop the needle making it leaner and moving the clip down will raise the needle making it richer. Be careful with the clip its small and if you drop it in a messy area, you probably won't find it.

  • digitalkidd

Posted September 24, 2007 - 12:16 PM

#13

It's hard to tell from day one because this is my first bike and I didn't know what was good or bad.......I think going from 32:1 to 40:1 is when I really started noticing it.

Should I go back to 32:1 and see if it gets any better before re-jetting?

  • Denn10

Posted September 24, 2007 - 12:47 PM

#14

32:1 is preferred for the lubrication that you get so it wouldnt hurt it to go to 32:1 and jet it, alot will tell you about mix ratios and how more oil is better and all that so you might see alot of different stuff about that but id say go with that and im sure you can get the jetting spot on with it.

  • digitalkidd

Posted September 26, 2007 - 05:31 AM

#15

I haven't had time to troubleshoot anything, but the more I think about it, the more I think it's the powervalve.

I changed my clamps and bars before my last ride and i remember yanking the crap out of the throttle cable to re-attach it to the throttle tube.

I remember pulling really hard one time on the inner cable with a pair of needle nose pliers when all of a sudden, there was no resistance.....I tugged a few times and then the cable snapped back, or retracted back to where it orginally was.

Does this make sense, or sound like something that could could possibly damage the powervalve?

  • mxjosh

Posted September 26, 2007 - 05:37 AM

#16

No, the throttle cable is not connected to the powervalve.

  • digitalkidd

Posted September 26, 2007 - 07:42 AM

#17

That's good to know - I guess I can rule that out as messing things up.

Thanks everybody for the help - I have to do the leg work now - Saturday is the plan.

  • Loaner

Posted September 26, 2007 - 09:16 AM

#18

I haven't had time to troubleshoot anything, but the more I think about it, the more I think it's the powervalve.

I changed by clamps and bars before my last ride and i remember yanking the crap out of the throttle cable to re-attach it to the throttle tube.

I remember pulling really hard one time on the inner cable with a pair of needle nose pliers when all of a sudden, there was no resistance.....I tugged a few times and then the cable snapped back, or retracted back to where it orginally was.

Does this make sense, or sound something could could possibly damage the powervalve?


This could affect throttle response though. Make sure the carb linkage is moving as soon as you move the throttle. You may have created some slack in the line. Check your cable routing and slack while your lookin around

  • BRM

Posted September 26, 2007 - 02:30 PM

#19

This could affect throttle response though. Make sure the carb linkage is moving as soon as you move the throttle. You may have created some slack in the line. Check your cable routing and slack while your lookin around


Understand what your saying here Loaner about the cable being damaged or the connection mis alligned but not to cofuse the matter there is NO linkage.

  • hobbs32

Posted September 26, 2007 - 02:48 PM

#20

The same thing happened to me with my yz250, I would sputter and bog until about midrange, and I pulled the cover off the powervalve, and a piece was broken in there. You can check if your powervalve is working by pulling the cover off on the right side of the cylinder, there is an L joint in there that connects to the powervalve. You will have to pull your pipe off then put it back on, then start the bike and when you rev it up that L joint should move up at high rpms. If it doesn't move something is probably wrong with the powervalve.





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