Hobbies Cars & Motorcycles How to Set Ignition Timing Share PINTEREST Email Print Tanya Constantine / Getty Images Cars & Motorcycles Cars How Tos Buying & Selling Basics Reviews Tools & Products Classic Cars Exotic Cars Corvettes Mustangs Tires & Wheels Motorcycles Used Cars SUVs Trucks ATVs & Off Road Public Transportation By Matthew Wright Matthew Wright has been a freelance writer and editor for over 10 years and an automotive repair professional for three decades specializing in European vintage vehicles. our editorial process Matthew Wright Updated May 24, 2019 Ignition timing can seem like a voodoo science to many do-it-yourself mechanics. Even wrench turners who consider themselves fairly adept under the hood will sometimes give you a strange look when you ask them to explain ignition timing, or ask if they time their own engine. The ignition system is fairly basic, but when you start throwing terms like Top Dead Center around, some people make a fast run for the repair shop. Truth be told, you can really make your car underivable in a hurry if you do a bad job adjusting your timing. Get it off by a little, and it might not start, or it might run rough, or you may even end up with an engine that is running unexplainable hot due to being poorly timed. If you get the timing too far off, you might even get some fireworks in the form of massive backfiring when you turn the ignition key! If your ignition timing is off, you'll know it. Or will you? Timing that is way out of adjustment will result in a poorly running vehicle, especially at idle. Your idle speed will be choppy or low. But there are other things that can be caused by a poorly timed engine. Hard starting, slow acceleration. The ignition timing procedure below relates directly to a Mazda 323 with a 4-cylinder engine. The procedure remains the same with most engines from that era -- roughly the '80s. Modern engines can't be timed the old way, and really old engines are timed by rotating the distributor to change when things happen inside the engine. But for an '80s fuel injected vehicle, you can use this procedure as a guide and consult your vehicle's specific repair manual for a more detailed description of your vehicle, including specifications for the adjustments. Ignition timing procedure Warm up the engine to normal operating temperature. Turn all electrical loads off. Key in the OFF position, lights off, flashers off, etc. Disconnect the vacuum hoses from the vacuum control unit and plug the hose. Connect a tachometer to the engine and connect a jumper wire between the test connector (Green 1-pin) and ground. Check the idle speed. The idle speed should be 850150 rpm. If the idle speed is not to specifications, proceed as follows: Remove the blind cap from the air adjusting screw and adjust it. After adjusting the idle speed, install the blind cap and disconnect the jumper wire from the test connector. If not already done, remove the wire from the test connector. Connect a timing light to the engine and check the ignition timing. The initial timing should be 12°11°BTDC (Before Top Dead Center). If the ignition timing is not within specifications, loosen the distributor body installation bolt and adjust the ignition timing by turning the distributor. Connect the vacuum hose to the vacuum control unit. Connect a jumper wire between the test connector (Green 1-pin) and ground. Ensure that the transmission is in neutral, then check the idle speed. The idle speed should be 850150 rpm. If the idle speed is not within specification, remove the blind cap from the air adjusting screw and adjust it. After adjusting the idle speed, install the blind cap and disconnect the jumper wire from the test connector.