YBR 125 Losing revs and stalling when idle.

[Yosh]

Recently my YBR has started stalling when idling and losing power after about 5-10 mins.

The only way I can stop it stalling is to keep revs very high. The first couple of times it stalls it can be started ok, after that it struggles starting then wont no matter what.

It doesn't matter if I use electric of kick start. But if I leave the bike for half hour or so it starts first time and has power for 10 mins or so again.

When starting initially, it starts perfectly first time and can be turned off and started again several times without a problem.

I'm still new to motorcycling and trying to learn how to maintain my bike. I'm guessing the engine might be fuel starved but if someone with experience has any different ideas it might help. (air filter has recently been replaced)

I'm planning on checking the fuel lines to see if anything is blocked, are there any obvious things I should or should not be doing/checking? Beside having a fag hanging out my mouth are there any important safety tips?

[Yosh]

Or are there any other suggestions what might be causing the stalling?

[Teflon-Mike]

How old is it?
Is it carbed or Fuel Injected?
How many miles has it done?
When was it last properly serviced?

Sort of symptom you describe, of gradual power loss then stalling; to me doesn't suggest fuel starvation.

Pipe blockage; bike wouldn't start.
If it was partial blockage, choking flow to carb; then it would only effect the thing at full throttle or under more load, and it wouldn't just 'die' or cut out, it would 'hesitate' as it ran short of fuel; then as that 'flutter' slowed you, and let the float-bowl fill up at whatever rate fuel could flow, pick back up again.
If very bad, might start and idle, but 'bog' and refuse to take load when you tried to rev it or put it under load.

If its Fuel injected; then could be a problem with the throttle position sensor; believe they are simple carbon track jobbies that do do strange things when they start to get dirty and or break down... but not sure how well that matches your symptom.

What you describe; to me; sounds more like gross lack of maintenance and or inordinate wear, and the engine 'over heating'.

If the tappets haven't been adjusted for like, ever; then possible that bike will start and run fine from cold, but under load, as engine gets hot, clearances close up, holding valve off the valve seat, stopping the cylinder sealing properly, giving low compression; which would give gradual loss of power until the engine cut out. Leaving it to cool? Clearances open back up as metal contracts; you get compression back, and bike will run again, until hot and clearances close back up.

Likewise cylinder and piston rings; usually aluminium piston expands more than steel cylinder so clearance between the piston and cylinder get smaller as engine gets hotter; but you get a similar symptom; gap between piston and cylinder gets smaller, piston rubs on cylinder, making more heat; and the engine is actually 'siezing' very slightly; its like putting the brakes on, but not locking the wheel; the force between cylinder and piston is just high enough that it 'brakes' the piston, without stopping it dead; which is what you feel as loss of power, like dragging a brake; until it stalls; then when cool, clearance opens up, taking the brake off, letting engine run again, until hot enough to do it again.

Have you got a Haynes Manual for it?

I'd look at the routine maintenance recommendation and work my way down the list, eliminating variables and see if it goes away; if not, could be an over-haul is due, as damage has been done inside the engine.

COULD be something as simple as the spark-plug is old and worn out... but start at the top of the list and work your way down.
____________________
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Current Bikes:'Honda VF1000F' ;'CB750F2N' ;'CB125TD ( 6 3 of em!)'; 'Montesa Cota 248'. Learner FAQ's:= 'U want to Ride a Motorbike! Where Do U start?'

[Yosh]

Its 2008, fuel injected 16,000 Miles. The last time it was properly serviced was at approx 13,500 Miles. Which was about when I bought it in about August. I've got the Haynes so will work through the list and see where it gets me.

Thanks for taking the time to post Teflon, I've found lots of you posts to be very clear and informative.

[Yosh]

It sounds very much like the badly adjusted valve clearance would match the symptoms. I will check it out thanks Teflon.

[_Iain_]

Hi,

I did think that people would have issues with badly maintained YBR's.

https://www.bikechatforums.com/viewtopic.php?t=240845&start=0

Heres a guide on a full service, including valves, oil change, filters etc.

Worth a look
____________________
Please be aware that the above post may be full of complete nonsense.
Riding: '07 KTM Duke II, Baotian BT49QT-20 Driving: '88 Volvo 340

[Yosh]

Thanks Ian, your thread has already been useful, I've got a few good ideas from it. Painting the exhaust is on my list if I can ever find a way to remove a rusted exhaust to head bolts.

[Yosh]

I adjusted the tappets, they were way off. I'm not sure what the exhaust one was but the inlet was less than 0.05mm. After adjusting I tested it, turned on to the main road and it stalled at the same traffic lights as does each time I've tested it.

Oh well. next thing on the list.

[Yosh]

Took the throttle body off to give it a clean found that the line from the air filter to engine is pretty packed with white junk crap. I previously found it in the air filter box bit, cleaned it and it junked up again pretty soon. Hopefully it will make a difference, if not at least I've learnt a bit more.

Im assuming that some of that junk got into the engine so will find out how to clean that out. Might that have done any long term damage, I'm going to replace piston and cylider rigs when Im confident enough.