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My Engines Backfires
An engine can backfire for a few reasons.
1. Lack of fuel.
2. Improper timing.
3. Improper firing order.
4. Stuck or damaged valve.
1. Most backfire conditions are a result of a lean fuel condition. A clogged or dirty carburetor is a very common reason for backfiring. Water in the carburetor bowl will also cause a lean fuel condition. If you feel the carb is dirty or it has water in the boawl it should be rebuilt.
If the engine tends to backfire while accelerating you might have a bad carburetor accelerator pump. The engine requires more fuel then normal when it's cold or when you are accelerating. A choke stuck in the open position can contribute to backfiring.
Check the supply of fuel to your engine. Make sure the filters are clean, the hoses are tight and everything is in good condition with no air leaks or obstructions. Check your antisyphon valve too.
2. Improper ignition timing can allow the engine to backfire. Conventional (points style) distributers have a mechanical timing advance mechanism that can stick or fail. Even old worn pints can make an engine backfire. Remember... first set the points (dwell) and THEN set the timing.
3. If you have just changed your distributer cap or spark plugs and now your engine backfires, chances are good that you have crossed a couple of plug wires. Check your firing order and make sure the correct wires are going to the correct spark plugs.
4. Every once and a while an engine will develope a valve problem. Overheating or over-reving can damage a valve. Is the valves sticks open or gets bent or damaged it will backfire. The best way to determine the condition of the engines valves is to perform a Leakdown Test.
Backfiring is a very dangerous condition that can cause a fire and/or more engine damage. Don't keep running the engine if it keeps backfiring.
Boats can explode. Moving parts can rip off your fingers. Hot exhaust can burn you to the bone and props can slice you up. One spark near a battery can cause an explosion. You can never be too careful. Remove the battery from the boat before working with fuel. Always disconnect the batteries negative terminal first. Clean up any spilt fuel and let ALL of the fumes dissipate before installing the battery and starting the motor. Pulleys and Belts can grab your clothes and hair. Don't wear loose clothing and keep your hair up under a hat. Always wear safety glasses. Be smart.
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