Loss of power bike under performing

you have water in your electrical system ..the coils on cg are well known fro small cracks ..get a new one fit it should be ok /.....also spray wd40 on all electricals every couple of weeks especially under the tank

It is very difficult to tell if the air filter is blocked by just looking at it. You should follow the servicing schedule that Yamaha suggest, change the filters when Yamaha suggest, a blocked air filter may give the symptoms you have experienced.

sounds like you blew the piston or seals or gaskets , check compression and refigure.

Usually zmr dont have these kinds of problems.your engine bore is gone thats why your engine oil level is reducing.and the black smoke is coming out...usually these problem occur when you are travelling in higher rpm at lower gear...

please change the spark plug first as its life is over...dont listen to the mechanic and the battery should be in good condition

this sounds like a fuel problem , clean the carbs, but replace the plugs,airfilter and oil at the same time

I have been using Castrol Active (Grade - 20 W 40) in this bike and have never faced any problems. Do not use the Castrol Power 1. Also get the engine oil changed after every 2500 kms. (get it replaced after 500 - 600 kms during the 1st service and after that change every 2500 kms)

Start by checking the fuel pump,fuel filter and carbs.Renew the spark plugs if necessary

It all seems to be leading to fuel starvation. Have you checked the tank breather is not blocked which can be a small hole in the petrol cap or a tube from under the tank. It could also be a blocked fuel filter. There should be two. One inside the fuel tank under the petcock, another before the fuel pump. Here is the workshop manual where you can find all info you will ever need for this bike.
Hop this has been useful, rate me if it has...?
Thanks and good luck.
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your cdi unit is suffering a from power surge try to check the output power if it is stable.