Changing radiator would help only if your remaining cooling system is in ok condition. Stock Radiator Fan in carby cultus is also stupid get some better high speed fan..
About Exhaust Manifold cut the 2 extra pieces between the 3 runners.(don't know how to explain that correctly)
If you are in Faisalabad i can recommend you a good mechanic for carbeurator work..
Otherwise do rebuild your car's carbeurator from some good mechanic..
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