What Causes the Exhaust Pipe to Make a Puffing Sound?

[Graham]

Exhaust pipe puffing noises may be caused by individual exhaust valve erosion or poor sealing, individual intake valve sealing failure with severe air leakage, carbon deposits at the contact surfaces between certain intake/exhaust valves and their seats, zero clearance on some valve stems, uneven adjustment or blockage of one idle jet in dual-barrel carburetors. When engine speed increases, the relative air leakage rate of valves decreases, resulting in smoother engine operation and disappearance of the exhaust pipe puffing sound. After identifying the fault nature, use the single-cylinder cut-off method to locate cylinders with leaking valves. There are many reasons for valve leakage. To simplify diagnosis, first remove the valve cover and inspect the valve stem clearance of non-operating cylinders. If normal, proceed with valve lapping. Intake valves only cause cylinder misfire at low speeds when severely leaking, occasionally accompanied by carburetor backfire during driving.