My yamaha ybr 125 has developed a fault, as described posted in newbie section! Started to cut out while riding after a short stop, restarted while still moving. Now has begun to be hard to start. When starts runs sweet. 2006 standard carb version.

Sounds like a  dirty carb or a blocked fuel cap vent . Hard to say with so little info . I'd check those anyway . Could also be a blocked/dirty  fuel tank petcock .

Cleaned tank cap and filter, plus drained float valve but fuel kept coming through! Possible cause?

Stripped and cleaned carb. Started first click but failed on restart!

Last time you changed the plug.

 

Changed plug made no difference 

Rekon i have found fault, in the ignition coil. Intermittent so only option to change it!!

Well that made no difference! Fault same as before. Batt voltage ok, when it starts it runs ok for 2 minutes riding then cuts out. Reatarts and runs sweet! Then wont restart after turning off. Battery?

you really need to check if the spark has disappeared when it wont restart, perhaps the pulser coil is intermittently faulty? you'd need a workshop manual and a multimeter to check the resistance of this I 'd imagine

Is it flooding because of a badly set carb float ?

Is it a vacuum operated fuel tap

Brand new coil and lead fitted. plug cap in tolerance. Stripped and cleaned carb cehcked float and main jet set correct.

Is it a vacuum operated fuel tap

no. Fuel straight out of tank, through filter (checked) into carb.

As airhead said look here https://youtu.be/54mNJaAleCo

Sounds just like what your bikes doing.

Brand new coil and lead fitted. plug cap in tolerance. Stripped and cleaned carb cehcked float and main jet set correct.

no. Fuel straight out of tank, through filter (checked) into carb.

New coil, stripped and cleaned carb, new plug. So clean fuel line clean electrics except for ECU. Cant test that!

Right. Cured i hope! Spayed electrical contact cleaner spray into ignition block. Now starts each time and no stalls yet!