Can I install nano fuel economizer for carb type toyota 3A engine? Will it help to improve fuel consumption of my car without any issue?
Yes, you can install it, but no, won't do anything for fuel consumption. Carburetors don't automatically adjust themselves to take advantage of new fuel characteristics or other changes in the engine's combustion characteristics.
Nano fuel economizer does the same job that your engine oil does. So, if you regular put new oil in your car, you're already doing as much for performance and fuel consumption as this product will ever do.
Anything called a "nano fuel economizer" is almost certainly a scam. In general, any device that claims to increase your fuel efficiency (or your health, your sleep patterns, your audio quality, etc.) with nanotechnology, magnets, harmonics, crystals, infrared or ultraviolet waves, vibrations, ultrasound, polarization, or quantum anything, probably does nothing at all, but the sellers are trying to confuse or impress you with scientific-sounding words.