Why Does a Pull-Start Gasoline Engine Fail to Ignite and Backfire?
3 Answers
Pull-start gasoline engines fail to ignite and backfire for the following reasons: Gasoline Engine Connecting Rod and Crankshaft Seizure: This may occur due to the connecting rod and crankshaft seizing (bearing seizure) or carburetor malfunction. In such cases, it is advisable to seek assistance from a professional mechanic for repairs. Correct Starting Method for Pull-Start Gasoline Engines: First, turn on the kill switch, then close the choke, and finally pull the starter handle. This procedure prevents backfiring. Proper operation ensures better engine performance and extends the engine's service life.
Pull-start gasoline engines failing to start and backfiring is a common issue I've encountered over my years of car repair, mainly due to several key problems. First, the spark plug might be dirty or have incorrect gap settings, causing weak sparks that fail to ignite the air-fuel mixture, instead detonating in the exhaust pipe and creating loud pops. Second, a clogged or improperly adjusted carburetor can lead to an imbalanced air-fuel ratio—too rich causes flooding and stalling, while too lean results in misfires and backfires. Third, insufficient compression due to worn piston rings or faulty valve seals lowers the compression ratio, preventing ignition. Fourth, incorrect ignition timing caused by faulty control modules or trigger devices can lead to premature or delayed sparks, often resulting in backfires. My advice is to first check the spark plug for heavy carbon buildup and replace it if necessary, ensuring the electrode gap is set between 0.6-0.8mm. Next, inspect the carburetor for cleanliness and unobstructed fuel flow. Compression issues require professional measurement. For safety, avoid excessive pull-start attempts to prevent engine damage—seek repairs promptly to minimize losses.
Last time I spent ages pulling the starter cord on my lawnmower at home but it wouldn't fire up, then suddenly there was a loud bang, which really bothered me. Later I asked a mechanic and learned it was caused by backfiring due to improper air-fuel mixture. For instance, too much carbon buildup on the spark plug prevents a strong spark, causing unburned fuel to accumulate and then combust violently. It could also be a clogged air filter restricting airflow and creating an overly lean mixture. Another time, old gasoline had deteriorated and formed gummy deposits that blocked the fuel line. The solutions are actually simple: first check if the spark plug is dirty - clean it or replace it if needed (not expensive); then clean the air filter and carburetor to ensure proper fuel flow; in cold weather, fuel lines can freeze making starting difficult, so pay attention to storage conditions. Remember not to neglect safety precautions as explosion fragments could injure someone. Now I always warm up and inspect before each use, and the problems have decreased significantly.
