Guys my khyber is giving jerks from a long time. Its engine had been overhauled completely once almost 10years ago. One and a half month back the head was overhauled too. Valves and valve seats were changed along with new head gaskit. The car was giving jerks before the (head) overhaul and is givings jerks after it. 2 days before the head overhaul, carburator was overhauled with carburetor repair kit but went in vain.
After the overhaul I have replaced the plugs,distributor cap,rotor,sparks plug wires and igniton coil but no use, the car is still giving jerks.
In neutral the car accelerates fine. In gear when moving, when the accelerator is pressed hard the car starts giving jerks and gains rpm VERY slowly. Black smoke can be seen in the rear view mirror at this point. Today I floored the car but it gave heavy jerks and rpm did not increase much (black smoke too).
The car gains rpm comparatively quickly when very little throttle is pressed and gives lesser jerks.
I cannot figure out what is wrong nor my mechanic. In neutral the car accelerates fine.
One thing I have noticed is the accelerates better and causes less jerks when the coolants temperature is cold.
What could be wrong? Any ideas
P.s car is petrol only