HEEEELP!!!!

[Welsh1da]

I have a 2011 YBR 125, had it for 8 months with no issues at all (well maintained and looked after) and its driving me crazy (when I can drive it)

6 weeks ago, right out the blue, with no warning, the following happened.......I took it out on a cool evening and within half a mile at lower revs, especially when cruising at around 25-30mph the bike began to jerk which got progressively worse within a mile. Then the engine started cutting out when I was waiting at the lights. When I got going again, I revved the engine to accelerate, but the rev's occasionally went up but seemed to lose 'power' and the bike sounded 'throaty'. Only by quickly 'pumping' the throttle could I get the revs to 'catch' and keep it running. I found that only at high revs could I ride the bike as when they went low, it would cut out or try to. By the time I got home (bout 40 mins after all this started) the bike would barely start and when it did, the engine would cut out the moment I twisted the throttle.

So I took it to be repaired and everything they've done seems to fix the problem for a day or two, but the issue creeps back, though slightly less each time. I've seen 2 engineers and had 2 different opinions, see below to what's been done and yet to be done.

So.......still riding my bike today, this is what it does:

1. Occasionally cuts off in idle (rev needle keeps intermittently dipping till it cuts out as if being starved of fuel or misfiring)

2. Jerks in 1st and 2nd gear and seems to struggle to keep 'rhythm', as rev counter continually drops as if trying to cut out but doesn't quite get there.

3. Jerks badly in 3rd gear when cruising between 25-30mph.

4. Works fine at higher revs and speeds (over 4000 revs and 40mph), no problems at all.

5. Bike starts 1st time in the morning, but when it cuts out, sometimes have to give it a few goes.

6. using engine breaking at slow speeds I get a 'popping' noise from the exhaust.

Mechanic 1:

1. Replaced battery and rectifier/regulator (Chinese) and spark plug.....didn't work.

2. Adjusted valves.....worked fine for a day then same problems came back although not as severe.

3. Replaced clutch....worked fine for 2 days then problems crept back, again slightly less than before.

4. Replaced fuel pump....His latest theory as to what's causing this, currently waiting part.

Mechanic 2:

1. Says battery is not charging or holding charge and is borderline "weak/bad" on the gauge.

2. Says rectifier/regulator (being Chinese) is getting too hot and could be faulty.

3. Says fuel pump fine (or it would cut out every time the PSI drops and not intermittently)

4. Says likely the alternator needs "winding"/replacing as its not charging the battery.

So guys, who do you think is right, do you have any other ideas or has anyone else had the same problems with a working fix to report????? As I'm coming to the end of my rope with this. Cheers

[Grumpy Old Git]

Timing issue?

Does the bike have 'auto-advance/retard' ?

If yes - could be 'sticking'.

[Welsh1da]

Not as far as I'm aware, just your basic as they come Yamaha YBR125, with no fancy gadgets or perks. I got it for its simplicity, but it seems to be stumping everyone.

[Stu]

More than likely fuel pump

[Guest]

Have a look for air leaks in the inlet manifold.

[Westbeef]

The fuel pump is a common issue on these, did the guy replace it or is he awaiting the part still?

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[Welsh1da]

Hey, parts in, going to have it done on Saturday. Frustrating thing is that none of the mechanics I've spoken to can settle on the cause of the fault, one thought it was the battery and regulator/rectifier, wrong!, then they thought it was the clutch, wrong! Now they think its a fuel pump, but this has been going on for 6 weeks, cost me lots of money (nearly £400) and when I take it to a new mechanic, he says pumps fine, it either works or it doesn't and says the alternator may be to blame..............Would give anything for someone to strip it and say Whallah! that's your problem £xx and it'll be fixed good as new......sigh

[Stu]

when I take it to a new mechanic, he says pumps fine, it either works or it doesn't

 

well thats utter crap on the YBR

its an intermittent fault on them and causes the symptoms you describe

[Westbeef]

I've had a quick Google and apparently the fuel pump can't prime properly when it's hot, which sort of lines up with the recent weather we've had.

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[Welsh1da]

Yeah I've heard of issues arising form hot days, but this originally happened on a cool night and now everyday whether its chilly or hot.

[Welsh1da]

Looking and googling each symptom its one or more of the following:

1. Return valve issue?

2. Fuel pump. (Awaiting replacement)

3. Regulator/rectifier. (Awaiting replacement)

4. Throttle shoes?

5. Electrical/ground wire shorting somewhere.

Any of that spark an "oh yeah could be" from any of you experienced chaps With the symptoms from the first post?