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Yzf R125 Bad Engine Work, Any Help?

Discussion in 'YZF-R125 Area' started by Rimas, Nov 10, 2020.

  1. Rimas

    Rimas

    Current Bike (Optional):
    Yamaha YZF r125
    Hello guys,
    From the start, i would like to mention, that english is not my first language, so sorry for any mistakes.

    My Yamaha yzf R125 2008, just before like 4days ago,developed problem: strange engine work.
    When it starts cold, it works like a charm, but after like 30seconds, when engine reaches optimal work tempreture, it starts acting strangly. drops his RPM to about 1.3k (when in the middle of the summer it was like about 1.6k).
    Also it sounds like he is chocking and automaticly he dies.

    Although it works (well kinda works) when i throttle up abit, to around 2-3k RPM, but when i want to move forwards it also chockes.

    So i would like to ask:
    What could be the problem?
    Is it expensive?
    Did someone faced this problem?

    Thank you for your answers and support,

    Rimas
    AxionUK and NorthCust like this.
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  3. NorthCust

    NorthCust Active Member

    Home Page:
    Current Bike (Optional):
    2008 Yamaha R125, Gasgas TXT 280, Stretched Neos
    License Currently Held:
    UK Full Bike
    hiya Rimas, welcome to the forum :)

    does the bike give you any "engine check" lights (yellow flashing light) when you switch it on?

    how is your battery voltage? (e.g. 12.2v when bike is off, 13.4v when running)
    AxionUK and Rimas like this.
  4. Rimas

    Rimas

    Current Bike (Optional):
    Yamaha YZF r125
    No engine lights comes on, so thats a big nono from the start.
    But i should check it then, with battery, but could it be the problem?

    *problem update*
    When it comes up to the working tempreture and when i quickly give some gas, and my bike is on neutral, it also chockes up ://
    AxionUK likes this.
  5. shakal844

    shakal844

    Current Bike (Optional):
    YZF R125 (2015)
    check compression, valve clearance.
    AxionUK likes this.
  6. Rimas

    Rimas

    Current Bike (Optional):
    Yamaha YZF r125
    Few weeks ago i went to a mechanic for a valve clearance adjustment. Could have been that he really broke my bike?
    AxionUK likes this.
  7. NorthCust

    NorthCust Active Member

    Home Page:
    Current Bike (Optional):
    2008 Yamaha R125, Gasgas TXT 280, Stretched Neos
    License Currently Held:
    UK Full Bike
    is that when the problem started? I would think if it was a problem with what he'd done you'd know pretty much straight away surely?
    Rimas likes this.
  8. Rimas

    Rimas

    Current Bike (Optional):
    Yamaha YZF r125
    You see, to be exact with the dates, it was fixed/checked by a mechanic 2020-10-02, and it occured just 2020-11-02. I drove whole season without any kind of similar problem. It must be some kind of coincidense, shouldnt it?
    AxionUK likes this.
  9. NorthCust

    NorthCust Active Member

    Home Page:
    Current Bike (Optional):
    2008 Yamaha R125, Gasgas TXT 280, Stretched Neos
    License Currently Held:
    UK Full Bike
    tbh if you drove for a month and it was fine it's probably something else.. things do break occasionally.

    tbh I don't really have much to go on.. but you need air fuel and spark.. if it's not happy, it's got to be one of those...so start with the basics...like what's the battery voltage (should be ~12.x volt not running, ~13.6-13.8 volt when running)., maybe have a look at the spark plug colour - that might tell you whether the motor is unhappy. and if all those thigns are fine then you know it's ok to look elsewhere... but there's no point pulling the engine apart if it's just your battery which has just died and then things aren't getting the correct power.. and don't run right.

    Compression check too like shakal suggested, though it's very tight in there and my comp tester doesn't fit so if you have one whcih does then I'd like a link to buy one too.. ;)
    Rimas and AxionUK like this.
  10. AxionUK

    AxionUK Member

    Location:
    Leicester
    Real Name:
    Maks
    Current Bike (Optional):
    Yamaha YZF R125 (2008) - Purple
    License Currently Held:
    UK Provisional (CBT)
    Hiya, I see everyone started to jump straight to the worst assumptions as per ;)

    You say it idles at 1.3k after warmup, afaik the engine starts off at higher rpm for the first 10-20 seconds to help it warm up and then drops to a lower idle. The first thing you should check is your idle screw, it's located above the throttle cable at the throttle body (just google yzf r125 2008 idle screw) and see if it's screwed in pretty deep or if there's space for it to be unscrewed slightly. If you are still able to unscrew it slightly then obviously just adjust your idle rpm to be at 1.6k or more - 1.3k is way too low so no wonder it dies. Do the adjustment after the initial rpm drop off.

    Now as for the stalling issue when moving off, I obviously have no idea how long you've been riding or anything like that, however I don't like to jump to worst conclusions. Could it possibly be that you're just letting out the clutch too quick or not giving it enough gas? Not trying to be mean and undermine your riding ability, please don't get me wrong :D
  11. NorthCust

    NorthCust Active Member

    Home Page:
    Current Bike (Optional):
    2008 Yamaha R125, Gasgas TXT 280, Stretched Neos
    License Currently Held:
    UK Full Bike
    >> he first thing you should check is your idle screw,

    ah yes good thing to check. you've just gone through this too haven't you.
    AxionUK likes this.
  12. misiozol

    misiozol Active Member

    Temp sensor needs checking .
  13. shakal844

    shakal844

    Current Bike (Optional):
    YZF R125 (2015)
    Engine idle speed ==> 1350 to 1550 rpm.
    According to the book hayness.
  14. AxionUK

    AxionUK Member

    Location:
    Leicester
    Real Name:
    Maks
    Current Bike (Optional):
    Yamaha YZF R125 (2008) - Purple
    License Currently Held:
    UK Provisional (CBT)
    shakal, colour me impressed if you know a 2008 yzf that runs at 1350rpm without sounding like it's about to give up on life
    NorthCust likes this.
  15. NorthCust

    NorthCust Active Member

    Home Page:
    Current Bike (Optional):
    2008 Yamaha R125, Gasgas TXT 280, Stretched Neos
    License Currently Held:
    UK Full Bike
    >> Temp sensor needs checking .

    I thought temp sensor but wouldn't that usually throw a fault code?
  16. misiozol

    misiozol Active Member

    No if its showing false data could be showing that there is -30 or 50 this would NOT bring code, if this is OK then TB needs to be checked .
    NorthCust likes this.
  17. Rimas

    Rimas

    Current Bike (Optional):
    Yamaha YZF r125
    The CPU of the bike doesnt give an error about any of the sensors or anything. Answering to one of you, i dont think that idle screw would help, becouse the problem continues thru out the drive, once in a while bike chockes on like 2nd gear (20-40km/h) or even 4-5th gear 50-60km/h.

    Thanks to all of you for trying to help me :)))
  18. AxionUK

    AxionUK Member

    Location:
    Leicester
    Real Name:
    Maks
    Current Bike (Optional):
    Yamaha YZF R125 (2008) - Purple
    License Currently Held:
    UK Provisional (CBT)
    That's fair enough, I'll leave it to the professionals then :D
    PS - I'm pretty sure you're not meant to go 50km/h in 5th gear :?

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