why my 120y fuel consumption so high?RM10=50km,100% city drive,i tot 120y is a car that save fuel.normally i change my gear when rpm reach 2.5~3.my 120y no power and engine sound very loud and noisy,why like tat 1?my 120y all is original part,never modify anything.i already overhaul but the situation still same.any one can help me?

how to set the original Carb and A/F ratio setting?

thats odd 120Y's seem to never run out of fuel. something wrong with the carb I think. have you got a 120y owners manual?

Thats about the same milage I get out of my datsun 120Y. As for the hoise, maybe u have a leak in the exhaust system.

RM10 --> 5.208 L of petrol

the best i got using stock carbs on A15 was 12.8km/L

malaysia fuels are dirty.

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You say that the engine is loud & noisy, but you don't say what kind of noise. Mechanical noise? Exhaust noise?
Your driving style seems just fine but have you given the engine a full tune up exactly as per the book. If the timing is retarded, you will loose power & fuel consumption will increase.
If the timing is too far advanced, you will loose power & fuel consumption will increase along with detonation which will make some noise.
If the carb is not secured to the manifols it can suck air causing a lean mixture, low power & a whistling sound. The low power causes drivers to use more throttle & lower gears which leads to increased fuel consumption overall.

Is the choke in the carb opening all the way?
The only adjustments that are provided on the carb are idle mixture & idle speed & I don't think that these are the cause of your problem.

You say that you already overhaul, but you don't say what you overhauled. The carb? the engine?

More information is needed in order to help you more.

If you give it a full tune up, just like the book says, tappets, points, [set dwell, not point gap] ignition timing at the correct idling speed with vacuum hose disconnected & plugged, [refit hose after doing the timing] set idle speed & mixture.
Does the vacuum advance work as it's supposed to? If not, then you will not get best fuel economy when at light throttle

If it's still no good, then something is very wrong & needs to be diagnosed & fixed.