Troubleshooting Outboard Motor Magneto Ignitions Application Note
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Troubleshooting Outboard Motor Magneto Ignitions Application Note Coil 23 SERIES II MULTIMETER kΩ Introduction Flywheel 10 20 30 40 OFF V Your outboard motor won’t start. V 300mV Yes, its been in storage for awhile but it was running well when you Primary Secondary A A left it. Should it go to the repair PRESS RANGE AUTORANGE 1 SEC shop? The shop will do a good job TOUCH HOLD 10A V but they’re always busy and the ! 100V 300 COM mA 750V repair will probably take two FUSED weeks —remember your out of town guests want to go fishing tomorrow. Isn’t it time you learned how to Breaker fix it yourself? You suspect the igni- Points tion since that’s what went bad last time. Will you need the special test equipment called out in the repair Condenser manual? NO! This application note will show you, in a few simple Engine Block steps, how to pinpoint magneto ignition troubles quickly. All you will need is a few mechanics’ tools and a good quality digital multimeter. Won’t start scenario Troubleshooting procedure You can justify the multimeter Now let’s get down to cases with We will assume you have already because it will do double duty for the dead engine. In order to start, tried the normal starting procedure, your other electrical troubleshooting the engine needs three critical i.e., turned the engine over a num- tasks, including the battery and items: a) proper amount of fuel/air ber of times, first with choke closed charging system, trailer lights, mixture, b) properly timed spark and then open. corrosion protection system, and and c) some compression. If it won’t other electrical systems in either start, chances are that one or more Spark plug check your house or boat. of these is missing. The trouble- The ignition troubleshooting Remove the cowling (if necessary) shooting logic is straightforward: procedure that follows can be used to gain access to the spark plugs. find out which critical items are for any small one or two cylinder For a twin cylinder engine, label missing and why. gasoline engine that employs a the spark plug wires so that they Before getting into the actual breakerpoint magneto ignition; for can be replaced in the correct procedure, verify that the fuel tank example your lawn mower, order. Pop the wires off and has sufficient quantity of fresh fuel chainsaw, generator, pressure unscrew the spark plug(s). Keep mixture and if your engine has an washer etc. track of which plug came out of electric starter, use the dc volts each cylinder. function on your multimeter to Now, examine each plug care- check the battery voltage and the fully. This is like palm reading; the ohms function to check the cables condition of the plug tip can tell a for loose or corroded connections. story about what is going on in With reference to the ignition each cylinder. If the plugs are wet system, here is a list of the critical with gasoline, fuel is undoubtedly components listed in the order of reaching the cylinders. their likelihood of failing: If the plugs are dry, the opposite Spark Plug, Breaker Points, Coil, HV is true. Look for a blockage in the Wire, Condenser and fuel system or a bad fuel pump in a Flywheel Magnet remote tank configuration. If the plug(s) are fouled with and coil to the engine block. This Coil carbon and/or oil, several things can be checked without taking 23 SERIES II MULTIMETER could be wrong: The spark to the apart the magneto as follows: Set kΩ Flywheel 10 20 30 40 Ω OFF V plug(s) is weak or nonexistent, the the multimeter into the ohms ( ) V spark plug heat range is too cold, function. Use the range button to 300mV or the engine has been run for long manually select the 40 kΩ range. Primary Secondary A A PRESS periods of time at low speeds (Auto ranging may not work here RANGE AUTORANGE 1 SEC TOUCH HOLD possibly with an incorrect fuel or due the inductance of the coil). 10A V ! 100V 300 COM fuel/oil mixture. In the case of Now, touch one probe tip to the mA 750V FUSED multi-cylinder engines, if only one engine block and the other to the plug shows difficulties, the problem metal connector inside the plug Breaker is likely to be a weak spark from wire cap. The meter should read Points the ignition system. the resistance of the coil and HV In any event, the next step is to wire in series. Good readings will Condenser check actual spark plug operation. range from 3 kΩ to 15 kΩ. Higher If new plugs are available, use readings mean a poor connection, Engine Block them for the next test. If not, clean which typically occurs either where the old ones as follows: using a the HV wire connects to the coil or Figure 1: HV wire resistance/continuity test sharp object such as the point of a at the other end where the HV wire Coil safety pin or a straightened fish connects to the spark plug clip SERIES II MULTIMETER 23 hook, scrape off the deposits on the inside the cap. A reading of OL kΩ 10 20 30 40 insulator that surrounds the center means an open circuit or break in OFF V V electrode. Dig down between the the electrical path. If a bad reading 300mV insulation and sidewall and remove is indicated, double check to make Primary Secondary A A PRESS as much carbon as possible. Now, sure you are making a good con- RANGE AUTORANGE 1 SEC TOUCH HOLD wash out any remaining oil or nection with both test leads. 10A V ! 100V 300 COM mA 750V carbon particles with a nonconduc- FUSED tive solvent such as paint thinner or Coil and HV wire continuity unmixed gasoline. Allow the plug to test for two-cylinder engines air dry; blow on it if necessary. If you are testing a 2-Cylinder, Next, gap each plug by tapping 2-Cycle engine (mixed fuel) then or bending the outer electrode. If perform the test as above for each you don’t know what the recom- cylinder individually. Look for a mended gap is, use 0.025" (a bank correlation between a bad reading credit card is typically .030"). Test Figure 2: Resistance/continuity test for 2-cylinder, (OL) and a fouled spark plug on the each plug and HV wire combination 4-cycle engines same cylinder. by connecting the wire to the plug If the engine is a 4-Cycle model and laying the plug on the engine (unmixed fuel) such as a Honda or Coil block where the gap can be seen. Onan, the test is performed slightly The plug outer body needs to make differently as shown in Figure 2. electrical contact to the engine Here we will be looking for conti- block as it does when it is screwed nuity from one spark plug clip to in place. the other since there is only one Now, turn the engine over at secondary coil which is not normal cranking speed and watch Primary connected to the engine block. An Secondary for a spark. If you are in bright sun, open spark path will kill the spark you may have to shade the plug to to both cylinders. see the spark. If this test shows no spark or a weak spark, troubles HV circuit repairs with the breaker points or coil inside the magneto are likely. A break in the HV circuit can occur in several places as shown in Coil and HV wire Figure 3. resistance/continuity test If the poor connection or open Figure 3: Possible locations of breaks in for one-cylinder engines circuit occurs at the spark plug clip, secondary HV circuit you may be able to repair it without The next test checks for a continu- taking anything else apart. If the ous path for the spark through the problem is located inside the mag- HV wire and the ignition coil. Refer neto, it will probably be necessary to the electrical diagram in Figure 1. to remove the flywheel. Note that for a one cylinder engine there is a direct electrical path from the plug cap through the HV wire, 2 Fluke Corporation Troubleshooting Outboard Motor Magneto Ignitions Coil The preferred cleaning method 23 SERIES II MULTIMETER is to scrape the contact surfaces with a sharp carpet-layer’s knife, 10 20 30 40 Flywheel OFF V followed by a wiping with solvent V 300mV on a clean cloth. Filing will some- times work but there is a risk of Primary Secondary A A PRESS damaging the underlying metal RANGE AUTORANGE 1 SEC TOUCH HOLD 10A V which will shorten the life of the ! 100V 300 COM mA 750V contacts. In any event do not use FUSED sandpaper. The grit will imbed itself in the contact metal, render- Breaker Points ing the points useless. If you want a quick fix to get the engine running, try the “old-timers Condenser Engine point cleaning trick” as follows: Block With the crank shaft positioned so that the points are closed, pry the Figure 4: Breaker point contact resistance test breaker arm open and insert a clean business card between the Breaker point test Measure the contact resistance contact surfaces. Release the breaker arm so that the points grip The breaker points on a magneto as follows: place the multimeter in the end of the card and then drag ignition are often located under the the Ω function and hold the probe the card through its width, wiping flywheel.