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Apr 08

Posts: 1068

geoffart says:

YBR engine issue.

Hi there,



I have a YBR125 06 model (carbed)


It has developed a little problem, where it likes to stall when the revs get too low (idling). 

So, if I start the bike with the choke, it runs fine... then keeps running as if no problem... but if I take the choke off it stalls straight away.

The bike doesn’t seem to have lost any noticeable power when at top speed (it was always gutless... but then it is a 4-stoke 125).

It does the same top speed it always did 50-60mph on a run. 

As I say, with the choke open it will keep the engine running without any throttle, but if the choke is disengaged, the bike will stall at the lights, if I don’t keep the revs above idle (that means keeping the throttle slightly open).

Major bummer, as was a lovely little bike until this happened... hence mightily grateful of any advice.

It's ex courier, but has been well looked after during that time... however it does have a lot of miles on the clock.  

The problem appeared suddenly after the bike had been left outside in the rain... although that could be purely coincidental.  What do you think?

Thanks for your input.



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  • Posted 3 years ago (10 June 2012 10:05)

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Aug 02

Posts: 3285

eatcs01 says:


Pick the tickover speed up by tweeking the idle adjuster nut.

What speed is it trying to tickover at anyway??

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Aug 09

Posts: 2721

MarcusMarsh says:

YBR Engine

Try the simple approach first.  As the bike has no other problems and runs well other than the stalling just turn the idle speed up a little and see if that solves your problem.

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Apr 08

Posts: 1068

geoffart says:

idle speed

Hi, thanks guys!

I cant really know what its idling at, because it just stalls as soon as I close the throttle, if stationary and if I fully disengage the clutch.

I'll try turning the idle speed up then.

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Mar 09

Posts: 9015

jaffa90 says:


The pilot jet controlls the ammount of fuel mostly up to 3,000rpm providing air is not going in where it shoudn`t.

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Apr 08

Posts: 1068

geoffart says:

still a problem.

Hi again,

Engine tick-over increased, so engine doesnt (always!) stall when idling. Thing is engine revs are not stable and engine used to run fine at lower revs. Engine Now idling at 1500-2000 rpm. Engine is unstable even after being placed on idle after a long ride . ie revs are slightly increasing and decreasing.

Dont think it's meant to be like that?  Could it just be blockage or something?


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Nov 07

Posts: 2432

smidget says:

Hi geoffart

You are describing a classic case of 'hunting' check air cleaner is free of dirt, set carb jets to workshop manual given settings then try the bike. 

If this fails then the best way round this without having to do the job more than once is to remove the carb, strip and clean, check all parts are serviceable (within tolerances) reassemble, set jets to basic settings, (to be found in workshop manual) ensure the air filter and inlet tract is not blocked. statr bike and get it to optimum running temperature, and finally adjust mixture screw.

Mixture screw adjustment, raise idle screw to about 2000 RPM and screw mixture screw in both direction a small amount at a time until highest engine speed is achieved set idle to manufacturers specification.

Good luck, hope you get it sorted easily and soon and keep us informed of what you find / do.

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