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Random massive deceleration at high revs, please help! (YBR 125)

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Hope I'm not breaking any rules by posting here i've just got a mysterious issue with my bike that I need to fix urgently and thought it would be worth posting here to ask for advice. 

In short my YBR 125 Custom (2016?) is having an issue where randomly (always over 7,000 rpm in 5th after 2 minutes or so) a massive amount of engine braking will kick in and the engine light will continuously flash (No code just constant quick flashes till the breaking stops). This will deceleration will happen for a seemingly random amount of time.

This issue has resurfaced multiple times over the past year of me owning the motorcycle and it has me and my mechanic step-farther stumped. The urgency is due to me starting work 50 miles away at a covid testing center on the 21st with no other means of transport there.

For a brief timeline this first happened in January before replacing the ignition barrel, spark plug ad neutral switch (in order to fix other issues). This seemed to solve the issue for a month before it happened again, potentially solved by returning the original spark plug yet I cannot remember if other things were also done that may have made a difference. Move forward to last month or so, the issue happens again. I order new spark plugs and replacing seemed to have fixed the problem entirely however 4 days ago it has returned, the new spark plugs are NGK/CR6HSA (as mentioned as the proper plugs in the manual) however the one that came in the bike when purchased is a NGK/CR7HSK. Today we replaced the ignition coil as the resistance on the original was a little high to that stated in the haynes manual, no difference was made.

The bike has done 14,000 miles, oil levels are good and the bike is started every two days minimum. It is also regularly ridden at 5th at full throttle for long periods of time. 

Is this a common problem with these bikes? Is there anything I might be able to check or common causes of issues like these ?

Any help and advice is greatly appreciated.

Edited by aj-1
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If anyone's reading this in the future it was fixed by using a brand new NGKCR7HSA from Halford's instead of a NGKCR6HSA.

No clue why as both the Haynes manual and owners manual reccomend a CR6 spark plug. Parhaps all 3 CR6 plugs off Amazon were Chinese counterfeits or the CR7 is better for when it gets colder in the UK.

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Well done with the reply , 


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Yeah... Don't buy plugs off Amazon... If they look like a great deal, be suspicious..!


I'd be looking at what the actual difference is between those two plugs.

It may be that you just bought dodgy fake plugs, but it may be that the other plug is higher rated, which leads you to the question: WHY did someone put uprated plugs in the bike?
Better spark?
To solve a problem?

What I'm saying is: Just because the issue appears to be 'fixed', don't stop looking for the problem!

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