YBR ESD Power Loss

[jeffyjeff]

12 June 2026

https://live.staticflickr.com/65535/54575078048_e81c6eccd1.jpg

2015 YBR125 ESD purchased new (old dealer stock) in 2019, 23100 km on the odometer. The ESD model has a carbureted engine (Mikuni BS25) sold primarily, dare I say, in the third world. The Pakistani YBRs are ESD models as are YBRs sold in Central and South America, to my knowledge. No electro-mechanical issues other than a TPS replaced at 20800 km. The bike is well-maintained (over-maintained to be honest) and runs better than it did when new…up until yesterday.

I was riding on Moroccan highway N6. It was 35 degrees C, and I was about 60 km into my trip and riding at 80 kph. Several km after turning the fuel tap to "reserve", the bike suddenly lost all power. To wit: instantaneous loss of throttle response and uncontrolled deceleration. After slowing to around 60 kph, the power magically returned. I kept riding, and after an uneventful 10 km, I started to think, "maybe that was just a little hiccup, nothing to be too concerned over." Then it happened again. No hesitation, no stumbling, nothing to indicate that the carburetor was starving for fuel; just an immediate loss of throttle and resulting deceleration. I thought "ignition power loss," but then I noticed my high-beam indicator illuminated even as the bike was in the state of power loss. As I slowed, the power immediately returned when I downshifted from 5th to 4th. Well that's odd. The glitch recurred 3 times over a 12 km stretch, and each time I was able to recover power by downshifting, except the last time required two downshifts to third before power returned. Six uneventful kilometers to the petrol station, where I filled the tank. I rode twenty-eight kilometers to home (after filling up) without any recurrence whatsoever. I had the fuel tap on reserve most of the way to see if that might be a contributing factor.

The instantaneous onset of power loss suggests ignition system failure, but it is odd that downshifting the transmission could bring about such an immediate return of power; coincidence? Maybe, but I have never experienced a repeatable coincidence like that.

I would normally dismiss the fuel system as the cause due to the split-second onset of symptoms, but it is hard to ignore that the problem manifested shortly after turning to "reserve", and only occurred when the engine was drawing fuel on the reserve standpipe.

I'm in Morocco until September. When I return, I'll probably have a spare fuel cock and an extra ignition coil in my bag. In the meantime, I intend to keep the fuel tap in the reserve position to see if that makes a difference. I checked the fuel filter (part of the petcock) and it was unobstructed. Once I run the tank down to less than 5 liters, maybe I'll drain it and remove/inspect the petcock. Specifically, I will be looking for a crack, hole, or damage to the shorter standpipe.

If anyone can suggest actions or observations I might make in the meantime, I'm all ears.
Thanks for reading.
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History shows again and again how nature points out the folly of men - BOC

[stinkwheel]

Well, a fuel tap obstruction seems possible.

Or even vapour locking in that kind of heat with a prolonged ride (fuel in the float bowl boiling). Especially with a small amount of fuel in the tank to get heated up.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.