Very poor mileage of my Honda 125

[Xulfiqar]

In this type of situation you have to go for elimination strategy.

Put your Euro 2 carb on another bike (Euro 2) and see if it gives problems there.
You said there was another euro 2 standing there (i presume it had genuine carb) fitted on it you should have told the mechanic to fit it's carb on yours to absolutely make sure that carb is the problem. If the problem was solved then carb is the culprit otherwise there are lots of other things including the insulator, valves rockers arms..etc

To be honest i think the shaving of the head is causing the problem, i don't understand what people want out of their cg's. 2014 model and you had it's head opened on the advice of the mechanic. :S

Anyone correct me if i am wrong shaving means the dome of the head has been slightly deepened so that there is more space above the piston and the blast which takes place is more than normal. This would not only have a worse effect on the valves (which i personally thing are the reason) but also don't expect the piston to last much longer either.

Check your sparkplug as well......unstable rpm could also mean you are running lean (plug becomes whitish)
Although it looks highly unlikely as mechanic has tried different settings there.

shaving the head makes the combustion chamber smaller - which means that the compression ratio has been changed, as the head has a quicsent combustion chamber with offset plug - this can cause the engine to run hot and also ping or knock under heavy load.

[ab6666]

shaving the head makes the combustion chamber smaller - which means that the compression ratio has been changed, as the head has a quicsent combustion chamber with offset plug - this can cause the engine to run hot and also ping or knock under heavy load.

but the increased compression ratio will also provide increase power? what do u say?

[Xulfiqar]

but the increased compression ratio will also provide increase power? what do u say?

yes it does, but it also leads to an excessively hot combustion chamber and also requires a change in ignition timing and fuel type being used - specially on an aircooled engine.

was the combustion chamber measured after the work?

[mfdarvesh]

yes it does, but it also leads to an excessively hot combustion chamber and also requires a change in ignition timing and fuel type being used - specially on an aircooled engine.

was the combustion chamber measured after the work?

Probably not
I can share my experience in Islamabad/Rawalpindi, No Lath worker use bore gauge, they just put the new piston the cylinder and bore or polish with sand paper. For combustion chamber they only use their naked eye to see and put on machine for polishing. Therefore I always suggest to buy new Head and Cylinder from AHL - else only luck ..

[Xulfiqar]

Probably not
I can share my experience in Islamabad/Rawalpindi, No Lath worker use bore gauge, they just put the new piston the cylinder and bore or polish with sand paper. For combustion chamber they only use their naked eye to see and put on machine for polishing. Therefore I always suggest to buy new Head and Cylinder from AHL - else only luck ..

tools are expensive to buy? You can polish the head surface on a piece of glass - its easier and makes for a better finish.