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1998 yz125 wont hit powerband

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Okay so last night I cleaned my air filter and repacked my exhaust and my bike felt like it accelerated better and today I went to the track and it started in two kicks cold and it accelerated good and sounded great I Road a few laps and it felt perfect then I turned it off and went to get water then it started and I was writing again then I took a break and when I went to start it it took three to five kicks to start and when I started it it accelerated good then I Road it and the bike would not hit power band then me and my dad took the carb apart and cleaned it and check the reeds and the reeds we're perfect then I put it back in and it started doing the same thing I don't know what's it is I might take it to a mechanic

Edited by Kill_shot545

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Try changing the spark plug ?

Too much oil on the air filter ?

...could be causing an "oil slick"

getting pulled through the motor

and semi fouling the plug.

 

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5 hours ago, yamaha7654 said:

Try changing the spark plug ?

Too much oil on the air filter ?

...could be causing an "oil slick"

getting pulled through the motor

and semi fouling the plug.

 

The airfilter is perfect the spark plug was oily but i doubt its that because it was running good a while ago and most of the time I'm on the pipe also its an iridium spark plug idk maybe my jettings off but its strage that it would change when it was running perfect a while ago

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Broken reed , worn top end, stuck power valve, failing electrical component, leaking seals,could be a number of things.

 

If the plug is oily then it's running rich. That's a certainty. Has there been a recent change in temperature or humidity? Bikes run rich in the summer and need to be jetted slightly leaner to compensate. Is it smoking more then normal? Does the exhaust smell any different? How the transmission oil level look?

 

What exactly is the bike doing? Does it not rev up at all, does it sputter, does it cut out, be more descriptive of the actually issue. Simply saying it doesn't hit powerband doesn't tell us much.

 

 

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This has happened to me and my friends. Idled fine, runs fine once u hit power band it try's to die. Check all your jets. Happened to me at a track on my yz thought it blew up to just find a little piece o sand in the pilot jet. Ran perfect after that..?

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14 hours ago, Kill_shot545 said:

The airfilter is perfect the spark plug was oily but i doubt its that because it was running good a while ago and most of the time I'm on the pipe also its an iridium spark plug idk maybe my jettings off but its strage that it would change when it was running perfect a while ago

If your plug is oily it means it is running rich or that it has oil coming from the transmission.  if the day got warmer as  you rode it the jetting gets a richer feel to it as the temp goes up.  have you ever set the float on it? 

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Also check the powervalve

shafts under the rectangular

cover on the front of the cylinder

There is a steel pin pressed into

the side of the shaft that falls out,

and the valves can open and close

on their own

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Not the piston because i just replaced piston and cylinder it has around 15hours right when w its gonna hit powerband it sputters reeds arent broken just put boyeson carbon reeds last week its revs up perfect just when you try to put the power to the ground it sputters

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1 minute ago, Kill_shot545 said:

Not the piston because i just replaced piston and cylinder it has around 15hours right when w its gonna hit powerband it sputters reeds arent broken just put boyeson carbon reeds last week its revs up perfect just when you try to put the power to the ground it sputters

 

6 hours ago, ohiodrz400sm said:

Broken reed , worn top end, stuck power valve, failing electrical component, leaking seals,could be a number of things.

 

If the plug is oily then it's running rich. That's a certainty. Has there been a recent change in temperature or humidity? Bikes run rich in the summer and need to be jetted slightly leaner to compensate. Is it smoking more then normal? Does the exhaust smell any different? How the transmission oil level look?

 

What exactly is the bike doing? Does it not rev up at all, does it sputter, does it cut out, be more descriptive of the actually issue. Simply saying it doesn't hit powerband doesn't tell us much.

 

 

Haven't checked the tranny but ill do an oil change tmr

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On 6/11/2017 at 10:40 PM, Kill_shot545 said:

The airfilter is perfect the spark plug was oily but i doubt its that because it was running good a while ago and most of the time I'm on the pipe also its an iridium spark plug idk maybe my jettings off but its strage that it would change when it was running perfect a while ago

I had the exact problem you have and my bike ran great until mid ride the powerband gave out. Step.1 got a new piston but still wasnt there. Checked my reeds, no light through. Checked my crank which  was good. Powervalve was gunky since I run rich but was cleaned and no outcome. Re sleeved my top end no outcome. However I put my needle to 1 and put direct air in the carb from the gas hose started to kick in better but still was lacking. Then i got bigger jets. Now it screams better than it did. 

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I was going to say... just because the temperature and humidity changes outside should not change jetting that much and make it run rich..

Now if the air density changes a lot that can definitely affect jetting...

usually when it gets hot and air density goes up...so does the temperature of the engine and we usually run the engine richer...

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