YS125 2020 rough idlling then cuts out and rough accelera...

[sadGorilla]

Hello,

First post so I apolgise if there is a formatting rule on this forum.

I was wondering whether anyone could give me some insight on what could be wrong. To avoid wasting time I will just give the facts and will add anything else if prompted to.

I recently bought a 2020 YS125 that was sorn for 2 years. It ran fine for a day, then the next day gradually got worse and worse when riding until when came back home to eat something upon returning it could no longer maitain a proper idle, it felt like it was choking, cutting out shortly after. The throttle as well would sometimes be unresponsive, when attempting to rev the bike it would make sputtering sounds with the revs going up and down erratically.

New to this I put some injection cleaner thinking after two years I could of pumped some sediment into the injector. Nothing. I brought it to a mechanic who changed spark plugs, cleaned injectors, drained the fuel which was very poor (it looked blackish brown), gave it back to me but still had all the same problems. Gave it back to him for him to change the fuel pump, and still had all the same problem. Would not idle even when just stationary in neutral. The throttle problem has not happened to me again since taking it back. But will cut out and am too nervous to put too much strain on the engine as I noticed if I changed to 2nd or 3rd too early it would become unresponsive and I have to pull in the clutch bring the revs really high just to get output again from the bike which wasnt ever a fun experience.

Taking it back home I noticed a check engine light now appear. I have since bought a general diagnostic tool to see what it could be, after I tried connecting the diagnostic terminals together with a wire as I saw somewhere it puts into dealer mode and would flash in a way I could decode an error but it didnt work, it just made a spark. I bought some contact cleaner as I will attempt to see if there is any corrosion on the wires causing this problem. As I cannot understand how it worked perfectly for a day then all of this happening. The bike only has 4500 miles also the person this came from was a retired police officer so I doubt he abused the engine.

I would bring it to a yamaha specialist but they are very expensive and far from me and also just feeling a bit let down from my experience with mechanics as the one I used was just a bit too unbothered for me.

Im not sure if it is possible for me to attatch a video to show the problem. But regardless if anyone does read this and wants a video I will find a way to show it as it I assume a lot easier than decoding this ramble.

There isnt a lot of information about YS125 on the internet, but my next theory would be perhaps a sensor or wire corrosion, as the problem is quite intermittent. Sometimes it wont cut out on idle for a minute and a half, sometimes it needs 10 seconds. I should mention if I rev it really high like to 4000 double the idling revs it doesnt not cut out on me. I also notice no different when starting it on cold or warm.

I'll add any more info if people want it.

If anyone could point me in a direction I'd appreciate it so much.

PS attateched video of it cutting out but only letting one vid not the other where I show it not respond to throttle, video was taken the day it happened hence no check engine light as this only happened two days ago.

Cheers

[jaffa90]

( It ran fine for a day ), did the mechanic thoroughly clean out the fuel tank and the fuel pipe and pressure clean the injector and test it ? After this first day has the bike been rained on or power wash ?

[sadGorilla]

Hi, yes he told me had drained and cleaned the injector. Whether it was thorough or not I would not know. I would lead as to not thourough as they seemed very unbothered by it all. It has not been rained.

I would add yesterday I went on a ride. The bike works perfectly when going faster than 15mph or revs about 4000. I replaced the battery as I noticed it's resting voltage was only 12V, the new one is at 12.6V. I did a load test on it and noticed when the bike struggled the voltage reading would behave erratically. Usually go to like 9V but it wasn't very consistent. I will try and clean all the connectors I can find as the battery thing took me all of yesterday to figure out. I know little about mechanics but perhaps the regulator bringing voltage from battery is struggling or just dirty connection. Not sure?

Thanks for response

[jaffa90]

Make sure the battery is connected to the bike, also the regulator sends voltage to the battery. Google is your friend as well on here.

[Mysteriass]

The YS is basically a next gen YBR - They just changed some parts to be a twat.

The fuel injection equivalent of a choke is called a "fast idle". It might be that the fast idle isn't engaging / disengaging correctly. So it's like you're running on choke.

I'm GUESSING that the fast idle will work off the engine temperature sensor. If your engine temperature sensor is duff then the fast idle won't know when to disengage or worse it'll be intermittent... and the ECU would probably understand that it's putting out totally bogus readings (Out of range), hence the "dealer" light.

Swap out that sensor and see what it does then.

The sensor SHOULD be on the back of the engine cylinder. NOT the cam chain adjuster... the other one with a wire on it. Try disconnecting it for now and see what it does... you might have to manually fast idle the bike for a minute till it's warm if it'll start at all.

P.S - Telling you it came from a retired cop is probably the "garage humour" way of telling you it's stolen.

P.S 2 - The engine light should have a series of flashes. So many long flashes and so many short flashes. That's the engine code so you don't need a FI reader. Perhaps. That's how the YBR works but I can't be sure of the YS. So for example, if you get ONE LONG FLASH followed by NINE SHORT FLASHES then that's a code 19.

[Kawasaki Jimbo]

[sadGorilla]

Hi thank you all for the responses. Appreciate it.

I will answer chronologically:

1)Battery is connected to bike, I sprayed contact cleaner on any electric plugs I could find and cleaned it up a bit with toothbrush and let the contact cleaner evaporate. Will keep it in mind not sure what the best sources are to learn so far just using ai, google and yt. I looked at getting a haynes manual but only saw ybr but seen a lot of people saying they are the same bike so not sure whether to buy one of them.

2) Thanks this is quite interesting. This could make sense with the symptoms. I notice it makes no difference whether warm or cold to the bike the moment it has to idle its a roll of a dice whether it will cut off or not. Could I ask, how come this sensor doesnt intefere when I ride at like +15mph. Is the temperature of engine sensor data more essential to ECU at lower RPM. Dont want to waffle too much here so will stop. I will look know to find a diagram with where the sensor is and test it tomororw. Yikes I hope not, last thing I need is to find out its a stolen bike. The engine light is just on with no flashing. I saw someone where you could make it flash by connecting two diagnostic terminals with a wire on the bike but upon doing it I saw a spark happen and chickened out, not sure whether I fried the diagnostic port. Perhaps YS is different to precedent models.

3)I doubt they flushed the tank tbh, I havent checked the interior of the tank properly as everytime I try and use a light I cant see the interior properly as the petrol blocks the view. I will give a better go tomorrow. Yes that click is the bike it makes that sound consistently. Its unfortunate that the exact second that happens my friends dad makes a click sound as well with his flip flop. I can make a new video if the sound is a particular clue but just to explain better it sounds almost like a solenoid closing/opening. I got this one off ebay, I just searched yamaha diagnostic tool https://www.ebay.co.uk/itm/283628450894?_trkparms=amclksrc%3DITM%26aid%3D1110006%26algo%3DHOMESPLICE.SIM%26ao%3D1%26asc%3D264184%26meid%3D22df8f4f73cb4a47968b549b77140be8%26pid%3D101224%26rk%3D2%26rkt%3D5%26sd%3D283884711774%26itm%3D283628450894%26pmt%3D0%26noa%3D1%26pg%3D2332490%26algv%3DDefaultOrganicWebV9BertRefreshRankerWithCassiniEmbRecall&_trksid=p2332490.c101224.m-1 If this link didnt work properly just a very generic obd2 scanner for 30 quid.

The diagnostic tool arrives on wednesday so will update on results then.

Thanks all again.

[sadGorilla]

I unplugged temp sensor to test whether it was faulty. But engine would not start without it plugged in.

[Copycat73]

my 2p worth.
fuel filter blockage .. after pump before injector .. ie inline screen .. very small ..

Blocked defective fuel injector .. clean .. or replace ...
____________________
Whatever I post I have no citation and no intention of providing one..
caveat emptor

[sadGorilla]

Hi, fuel pump was replaced albeit with a used one. Would hope that this isnt the problem. The mechanic said he cleaned the fuel injectors but again in hindsight dont really trust anything that guy said, will consider cleaning it myself this weekend depending on diagnostic tool conclusion. Thanks for comment.

[A100man]

[Kawasaki Jimbo]

If there’s an engine warning light it’s got to be an electrical issue hasn’t it? That old, “blackish-brown” petrol might be a red herring.

[sadGorilla]

Lol. Diagnostic tool came back got five errors will lay them out sequentially in order it gave them to me:

P0108 - Manifold Absolute Pressure/Barometric Circuit High
P0113 - Intake Air Temperature Sensor Circuit High (Bank 1)
P0122 - Throttle/Pedal Position Sensor/Switch A Circuit Low
P0198 - Engine Oil Temperature Sensor Circuit High
P0511 - Idle Air Control Circuit

This all looks pretty daunting to me. I wouldnt have the slightest clue what all this means will try read up on it. Would anyone have any advice? Not sure whether this means I have to basically replace every one of these sensors which I'll do because I'm willing to do anything at this point just to get my bike working. Not sure if it is of importance but I did the test after leaving bike off the whole night and morning. Plugged in tool, turned key, and let the machine run.

Cheers all, immensely appreciate any help.

[sadGorilla]

Kawasaki Jimbo

I almost hope in a way I'd was told FI is able to stomach bad fuel relatively well. I would hope diagnostic narrows it down now exclusively to electronics.

[Kawasaki Jimbo]

Blimey, you've nearly got the full set there! Some of them could be historic or a consequence of unplugging stuff during maintenance. Now that you've noted them down I'd delete all errors, unplug, run the bike until the engine light reappears and then look again.

[Easy-X]

If everything has an error, might point to an earthing issue.
____________________
Royal Enfield Continental GT 535, Husqvarna Vitpilen 401, Yamaha XSR700, Honda Rebel, Yamaha DT175, Suzuki SV650 (loan) Fazer 600, Keeway Superlight 125, 50cc turd scooter

[sadGorilla]

Hi I just cleared the errors as you said ran 5 ignition cycles. But it keeps cutting out so badly i can barely keep an idle more than 5 seconds. I would say it noticably does a better longer idle when cold and left alone for a while. No engine light has reappeared since i just tried this 3 mins ago. I have cleaned ecu connector and some wires i found on the left hand side of the bike, they were all wrapped up in a rubber cover. I cant find multi-pin connector that goes into the throttle body chatgpt keeps telling me to clean.

How could I fix an earthing issue also?

[sadGorilla]

I checked the voltage across positive terminal to engine metal frame. 12.4V. Slight drop from days prior. But would argue earthing is not a problem due to this reading.

Tomorrow my last hope I guess is to remove everything including fuel tank, as much basically to look at this throttle body and see what could be going on.

[sadGorilla]

Quick update in service of those that will see this in years to come and want to know what my problem was to better understand if my fix could be relevant in fixing their bike.

Spark plug. The mechanic I had went to had put a spark plug meant for racing bikes as explained by the Yamaha specialist. Upon him putting the proper spark plug worked perfectly instantly. Why I encountered the problem to begin with I am not sure. Perhaps spark plug degraded. This doesnt seem to explain why I was getting fault codes about an array of things. Perhaps replacing throttle body which I ended up doing in the end was the correct decision. As I was getting a TPS value that said the throttle was always half open which I had to reset which didnt fix the problem. Not sure whether the ECU adapted to the poor plug manifesting then this TPS sensor. IDK but the bike works now and I wanted to at least provide an update as I know I looked at a lot of 10 year old posts that were useful. Cheers for the help

[Kawasaki Jimbo]

A TPS fault seems a more likely cause than a ‘racing spark plug.’ I see on your bike the TPS is part of the throttle body rather than being a separately available component. Anyway, happy days!