Yamaha YS125 issues with stalling when throttle pulled

[DannyCrooks93]

Hi gents, 

 

Been having on and off issues with my YS125 (2018 model!) and as a new biker or even vehicle owner and having taken it to garages a few times for this specific issue and nobody being able to find the fault or being able to replicate it, I am reaching the end of my tether with this bike being an issue since I purchased it last March.

 

Basically, the engine (typically when it's cold) will struggle to start and any pull on the throttle will cut it out. I've recently taken it to the garage for this issue specifically in which they charged the battery, changed the spark plug and cleared water from the air filter deposit. Taking it to the garage for my MOT, as I was walking away the mechanic tried to start the bike and had it struggle to start but nothing was said after I received my report. I did mention how I heard it struggle and he checked the battery voltage and that it's charging properly once started, which it was.

 

On the ride home, there was a sudden downpour which cut out the bike completely and leaving me on the road trying to get it back up and running for about 5 minutes in which it eventually did and started sputtering but eventually got some whammy in it and I was able to move off 

 

Same issue this morning however, cold morning with slight rain, bike turned on fine but as soon as the throttle was pulled, it cut out like it was stalling. It then struggles to start back up and just cranks continuously.

 

If anyone is able to help identify what to look for next, I have some time over the weekend to try and look into it but I'm not mechanically minded and being new to bikes, I don't really want to damage it further, thank you!!

 

Videos: https://streamable.com/ol6tbm & 

https://streamable.com/9o2bi7

 

 

Edited March 31, 2023 by DannyCrooks93

[Old-codger]

If  it cut out when it started to rain then water is getting at th ignition somewhere so try to dry all the connection blocks out check the wiring for damage or water ingress. Look at the HT lead and cap and dry out and seal lead and possibly change plug cap if it looks suspect. Dont understand why there was water in the airbox but check dry out if water in there and dry filter or replace. It may pay to drain all the petrol out of the tank as there could be water in there and carbs injection systems do not like droplets of water. Once you get the ignition dried out get a spray can of ignition sealer and spray on exposed leads and tape if anything looks bodged. If ts got a injection system it probably doesnt have a choke so the ecu will adjust mixture from cold. Look up the cold start procedure some bikes need the throttle closed others you have to open slightly, what does the manual say on starting.  

[Mississippi Bullfrog]

Stalling when ope ing the throttle often be weak ignition which goes with what has been said above. I second checking the lead, plug cap and plug. Any damp will cause problems.

 

Sometimes if you start the bike in the dark you will see the sparks tracking to earth. 

 

If in doubt replace the lead, cap and plug. A micro-fracture in the ceramic can cause issues. Sometimes just crud around the plug can hold moisture. 

 

WD40 is a water dispersant and can help prevent damp. 

[DannyCrooks93]

Cheers guys! Live in the UK and the rain isn't playing ball this week so I'll take a look when I can and give an update, much appreciated!

[DannyCrooks93]

Cheers for the replies guys,

 

Once the weather cleared up I was able to put some WD40 contact cleaner on any exposed wires not covered in casing as well as around the spark plug, gave it a slight tighten too 

 

Had no issue since! Thank you guys!