2010 Yzf-r125 Power Loss Please Help

Discussion in 'YZF R125 General Discussions' started by Luke Saunders, Feb 9, 2017.

  1. Sadly, still sat in the garage in bits.

    The bike ran flawlessly until suddenly something unexplainable went wrong.

    I still haven't found out what's wrong with the bike, for that matter; i dont have a clue. I've tried absolutely everything and as I said; every part of the motorbike works perfectly, but as a whole the bike does not. Still turns over without any issue, still doesn't start.

    Very sad times for me, it was my only transport. As I said, it's in the garage in bits. I'm soon to take the head off the engine and have a look inside, I'm thinking surely it's gotta be something major, so it should be obvious... right? Let's hope so, hate seeing my baby like that : (

    I'll update you guys when the next stage is over.
    James Will likes this.

  2. Long shot i know but going with my previous experience. i had the same problem with spark but no fire and after trying all that you have and giving up i took it to a local (old school) mechanic, who himself had it for 3 days before calling a guy that did bike electrics to run a diag and turned out it was a ignition Coil that cause my fault

  3. Hi guys, been a while since I updated this post.

    The patient has been sat in the garage for two months now, as I've found transport alternatives so haven't needed it 100%.

    I've been looking through similar posts and blogs of people who have had very similar problems.

    As a lot of you have read, I've checked pretty much the entire bike now:

    -New spark plug
    -New oil filter
    -New air filter
    -New oil
    -New fuel
    -Checked compression (all clear)
    -Fuel pump working perfectly and primes
    -No blockages at all on the injector
    -injector working fine
    -spark plug sparking, strong spark

    The only thing I haven't yet tried is replacing my battery. I hear these small 125 batteries only last about a year. I've had my battery for over a year and a half. It also loses charge excessively quickly.

    Whilst troubleshooting the bike, I had to frequently charge the battery (I assumed this was because I wasn't using the bike, but come to think of it; it loses charge VERY quickly.)

    I looked online for symptoms of a dead/dying battery:
    1. Your engine cranks but doesn't start. My engine cranks but does not start.
    2. No crank, no start, no lights! This one doesn't apply to me
    3. One day it starts fine, then next day it won't. Exactly what happened to me
    4. Cold cranking is hard work. Cold cranking drains my battery from full in about 10 seconds flat.
    5. You've jumped it a lot already. Jumping does nothing
    I've purchased a new battery, bought a Motobatt due to hearing good things about them. I'm praying it fixes the problem, if not it was worth a try.
    If this doesn't fix the problem, then I'll have to make a decision to either scrap it for parts or take it somewhere to get the engine out and take it apart.

    Again, can't stress how sad this is for me, bike ran fine no problems for a year and a half; then suddenly dies with seemingly no chance of resuscitation/

    Batt arrives tomorrow; I'll keep you posted.


  4. Update- I fitted the new battery, still won't start. Still cranks healthily but won't pull through...

    I got an LED endoscope from one of my friends and had a look down the spark plug hole...

    I could see the piston head as soon as I inserted the camera, and although it seemed fine, there's scratches all over the piston head and a small chunk of the piston head seems to be missing.

    It still doesn't make sense to me though, I would've thought it i'd blown apart my piston I would of at least heard it?
    As mentioned, when the incident happened, the bike just lost power and gently came to a controlled stop. Surely If I'd done some serious damage I would've either come off, or at least had rapid deceleration?

    Did a final last-effort attempt at bump-starting it, ran along at around 10mph and dropped the clutch, into first; still get that sound as if the bike wants to start, but won't.

    The aforementioned friend is coming to have a final look at it with the endoscope again in a few days, i'll give you all the verdict then.



  5. I had exactly the same symptoms as you years ago mate mine was the piston rings where shot. ..it's happened twice now both resulting in running low on oil.
    The only thing that got it running again was engine rebuild
    If yours has a chunk of the piston missing I'd say that's the cylinder dead and the cylinder head / valves dead mate and yes it can blow just a chunk and you won't notice it depending on how big the chunk is it may have fallen down into the internals which means a complete engine strip.
    I know you want it running mate but only a strip down now will tell you what damage has been done
    If you do strip get some pics up

  6. You are correct.

    Just rang up my local Yamaha dealership, I didn't have to say much before they told me it was low oil, which of course I know it was. I told him about the chunk of the piston missing, and he told me its far cheaper to just buy a new engine because its likely i've ruined the bore as well as the rings, valves, and potentially my gearbox via having very low oil.

    It's my fault, this was my first vehicle and I genuinely didn't know you had to oil changes (i know sounds retarded) but nobody ever told me.

    It's very sad, especially considering what I've spent on replacement parts to try and narrow it down...

    Oh well guys, I'm going to buy either an MT125 or YZF125 engine and do a swap.


  7. Don't beat yourself up mate these bikes are really oil thirsty I made the same mistake as you and we ain't the only ones it's a costly mistake but one we ain't likely to do again.
    I rebuilt mine with a 150cc just got to do the finishing touches then off for the mot
    Have look on ebay mate you can get a good engine for about 400 quid but keep an eye on the year as the new models fit but the exhaust port is angled different so it may need the exhaust as well
    Buy now you know the engine has blow strip it apart and have a look it won't do any harm
    Luke Saunders likes this.

  8. Cheers mate, appreciate the friendly advice. Yup i definitely will NOT be making this mistake ever again haha.

    Yeah, since i've got nothing to lose I'll be stripping down the engine tonight. First im just going to take the head off and see if the piston moves freely... Although the Yamaha guy seemed to know the problem straight away, it was an over the phone diagnosis, so potentially it could still be something else.

    Only one way to find out! - I'll update you guys tomorrow if the piston moves freely, I may just have a lack of compression due to rings or valves. New piston, heck, even new piston and bore will still cost less than a new engine for about £400... If I haven't damaged the gear box, then I might just get away with it. We'll see!

    Thanks again,


  9. Good luck mate just remember to get the timing correct lol I didn't and killed a set of valves and don't drop the timing chain inside the engine like I did
    I've stripped mine countless times mate if you get stuck give me shout

  10. Right, update time.

    So this is the week, it's finally here. I'm getting paid + a bonus so the bike is getting revived.

    I am not faced with a choice; as you all know I've done countless diagnostics and failed the fix the bike. I now have to choose whether to buy a cylinder kit and a piston kit (completely replace top end) or just buy a new engine altogether.

    The prior is obviously cheaper, but I don't want to replace my top half only for the bottom half to then die also, especially considering it was originally deprived of oil.

    The latter is obviously expensive. I originally wanted to get an engine with low mileage but unfortunately, my bike is pre2013 so few engines have low mileage.

    I need expert advice. Is it worth trying to fix my engine or should I ditch it and get a new one. Price difference steep. £200 for kits, £400-£500 for new engine.

    Cheers guys

  11. Hi mate
    It depends how much damage was done to the bottom end ...and if your willing to take the risk that there is no Damage.
    If your main aim is to get the bike working my advise is buy a complete engine it's a lot easier and less risk, I had to rebuild mine 2 times as I messed up the timing and then chain tensioner failed so it worked out more exspensive but I now have a 150cc I had to buy a power commander to get it running sweet though.
    If I had to do mine again I'd just buy a new engine it's a lot less hassle and there is a bloke on ebay that will swap eninges for a rebuilt one


  12. Yeah I've got a eeling I'll run into problems later which I'd really rather avoid.

    I've been speaking with the ebay bloke I believe you're talking about, sadly they're shut until june7th and wanted it done soon! Not many pre2013 engines for sale so its looking like ill go to them despite the wait.

    I just hope they don't mug me off and take my 14k engine and give me a 25k+ rebuild ; thats my only fear.

    You're right though, It's a lot less hassle and after 4 months of no bike... its probably worth the money.

    Thanks for your advice Jas! Gratefully accepted.

  13. That's a shame they can't do earlier mate I think a post 2013 engine will fit your bike but the gear linkage will need to be flipped and you will need the exhaust from the same year as the angle is off set mote than the 2013.
    If the engine only seized and not broke the piston then I see no reason why it can't be rebuilt.
    I rebuilt mine with a 150 for 130 plus 300 for the power commander and mine had seized twice lol but as i said easier and safer option is the new engine
    To be fair you won't know what millage it's done that's the catch with them
    Keep an eye on ebay I saw loads of pressure 2013 engines on there a fee weeks ago

  14. Yeah I'd really like to rebuild it but im scared i'll get it wrong and get more problems later on.

    I've been looking around trying to find the exact year the R125 got a facelift. Looking on Yamaha's website, I believe 2010-2013 were the same bike, and it got a facelift in 2014, because every model from then on looks different.

    I've found a decent 2013 engine on Ebay with low milage. If anybody knows for certain whether it'll fit that would be greatly appreciated!

    If the 2013 will fit then PROBLEM SOLVED. - I'll have a newer engine with low milage.. but the all important question: Will it fit?

    Thanks for the help Jas, but I've got a feeling you're a little bit more engine-handy than I am haha


  15. RPS

    RPS Member

    In Technical Discussions part of this site there is a chap who knows a lot about yzf engine problems and strips and rebuilds them. Might be worth asking his advice about your situation.

  16. As far as I know all the engines will fit the bike but with the newer bikes they have changed the gearbox and exhaust exit so you'd need to just flip the gear lever (easy fix ) and change the exhaust as the older model exhaust fitted means the fairing won't fit I'm pritty certain that buying the new model exhaust will solve that as well
    There is a post on here where someone has fitted a nee engine to an older bike
    I was thinking the same when I was looking for a replacement mate newer engine less miles and you'd get a better made engine as all the bugs would have been worked out by yamaha.
    As I said mate if I could go back and start it all again I'd just buy a replacement engine it's so much easier in the long run just make sure you fond out exactly why they are selling it as you don't wanna buy a dud.
    Rebuilding the engine isn't as hard as it's seems mate I was just stupid and skipped bits which cost me in the long run but even If your not mechanically minded you should be able to change the top end in about a day or 2 I just thought is dead anyway I may as well try ....but bear in mind I stored mine after it failed for 5 years lol only got the drive to try again last month lol irst click of the button she fired up so it is possible mate

  17. Thanks RPS I'll check him out...

    Thanks Jas, that is somewhat reassuring... I have a village mechanic, might be worth pulling the top off; as you said, might as well its dead anyway...
    I'll see if I can get someone to give me a hand tonight after work.

    1 problem, my exhaust bolts are seemingly rounded off/ corroded, so I cannot get the exhaust off. Should I angle-grind the bolts off or is there another way? Some kind of clamps I could put over? Cheers

  18. It's always worth a look mate
    If they have rounded I would use heat and a pair of grips I would cut them off mate as that will be a lot more trouble and cost speak with your mech mate bit I'd go heat and grips last resort I'd grind 2 sides smaller and use a smaller spanner

  19. Okay, did some stripping on the bike over the weekend. I've gotten the radiator off and almost all of the wiring harness. Just a few questions if anyone can help:

    1: There is a black wire going from the fuel pump/primer to the engine; I cannot seem to pull it off or loosen it... what is this and does it come off? If so, how?

    2: How to a remove the clutch + throttle cables? I'm assume i'll have to open up the handlebar levers? Or can I do it by where they meet the engine?

    Cheers guys, I've ordered the new engine it's on its way!! Just gotta wrangle out this old one first. Only things left are mentioned above + got to take chain off, then we're good to go!

    Also is it possible to purchase every bolt/screw/nut from the bike? Would be really handy because a lot of the bolts/screws and nuts are all starting to round off/corrode. Can I buy every bolt lol?

    Thanks :)


  20. Hey luke
    Good to see you've got a new engine
    The black wire if it's the one that goes to the intake body I believe there is a bolt that un does the injector that should release the wire
    The clutch is easy on the handlebars there is around nut where the cable goes in wind that so the cable goes slack then on the side of the engine theresults is a cable clamp that holds the cable Un screw the bolt to losses the cable then further down where the cable finishes pull the round bit real tight and remove the cable .....it's one of those cables that has a round bit on the end that needs the cable twisting and pushed through a slit in the holder but you will see what I mean when you see it.
    I've yet to find a whole bike kit for nuts and bolts only the fairing or mail engine bolts but you can but replacements easy enough

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