what is the best engine oil for a 1.6 L carburettor engine of ford laser 1991 done 300,000 kms with manual transmission and what else do i need to check at this stage?
Anything on the shelf in proper weight as they all exceed the spec required for a 1991 car.
Check your owners manual for the proper weight, check the spec like Andrew says and make sure the oil meets API SM etc. Almost all major brand oils on the market today meet or exceed the current specs
The best oil isn’t by brand, it is clean oil as in fresh oil from an oil change. A motor with a carb isn’t as efficient as a motor with fuel injection so I’d stick to oil changes every 3,000 miles and no more than 5,000 mile between changes. Carb’d motors get more raw fuel in the oil faster and therefore benefit from shorter oil change intervals.
What else to check? Did you just get this car? If you are a new owner I’d suggest getting all the fluids changed; manual trans fluid, coolant, brakes, power steering, everything. Check the drive belts and hoses for wear and soft spots. Find out if the motor has a timing belt and if it is an interference motor or not (go to Gates.com). If it has a timing belt and you don’t know when it was last changed you should consider having a new one put in.
Your owner’s manual will have all the things that need checking and replacing. With that many kms on it, I assume this is an Asian Escort, the cooling system should have been flushed and refilled THREE TIMES (every 100,000 km), you should be needing your 4th set of spark plugs and probably new wires.
The fluid in the gear box and differential (transaxle) should be changed every 100,000 km as well.
If you just bought the car, have the brakes checked and if OK, at least change the brake fluid.
If you live in a tropical country, you can use any car motor oil in grades up to 20W50, but I would only use that if the engine uses oil. Normally, 10W40 is good for tropical regions.