Troubleshooting Outboard Motor Magneto Ignitions

1 Application NoteTroubleshootingOutboard MotorMagneto IgnitionsIntroductionYour Outboard Motor won t , its been in storage for awhilebut it was running well when youleft it. Should it go to the repairshop? The shop will do a good jobbut they re always busy and therepair will probably take twoweeks remember your out of townguests want to go fishing t it time you learned how tofix it yourself? You suspect the igni-tion since that s what went bad lasttime. Will you need the special testequipment called out in the repairmanual? NO! This application notewill show you, in a few simplesteps, how to pinpoint magnetoignition troubles quickly. All youwill need is a few mechanics toolsand a good quality digital can justify the multimeterbecause it will do double duty foryour other electrical troubleshootingtasks, including the battery andcharging system, trailer lights,corrosion protection system, andother electrical systems in eitheryour house or ignition troubleshootingprocedure that follows can be usedfor any small one or two cylindergasoline engine that employs abreakerpoint Magneto ignition; forexample your lawn mower,chainsaw, generator, pressurewasher II MULTIMETEROFFV300mVAAPRESSRANGEAUTORANGE TOUCH HOLD10A300mACOMV100V750V!

2 FUSED1 SEC10203040 VPrimarySecondaryCoilBreakerPointsConden serFlywheelEngine Blockk Won t start scenarioNow let s get down to cases withthe dead engine. In order to start,the engine needs three criticalitems: a) proper amount of fuel/airmixture, b) properly timed sparkand c) some compression. If it won tstart, chances are that one or moreof these is missing. The trouble-shooting logic is straightforward:find out which critical items aremissing and getting into the actualprocedure, verify that the fuel tankhas sufficient quantity of fresh fuelmixture and if your engine has anelectric starter, use the dc voltsfunction on your multimeter tocheck the battery voltage and theohms function to check the cablesfor loose or corroded reference to the ignitionsystem, here is a list of the criticalcomponents listed in the order oftheir likelihood of failing.

3 Spark Plug, Breaker Points, Coil, HVWire, Condenser andFlywheel MagnetTroubleshooting procedureWe will assume you have alreadytried the normal starting procedure, , turned the engine over a num-ber of times, first with choke closedand then plug checkRemove the cowling (if necessary)to gain access to the spark a twin cylinder engine, labelthe spark plug wires so that theycan be replaced in the correctorder. Pop the wires off andunscrew the spark plug(s). Keeptrack of which plug came out ofeach , examine each plug care-fully. This is like palm reading; thecondition of the plug tip can tell astory about what is going on ineach cylinder. If the plugs are wetwith gasoline, fuel is undoubtedlyreaching the the plugs are dry, the oppositeis true.

4 Look for a blockage in thefuel system or a bad fuel pump in aremote tank Fluke Corporation Troubleshooting Outboard Motor Magneto IgnitionsIf the plug(s) are fouled withcarbon and/or oil, several thingscould be wrong: The spark to theplug(s) is weak or nonexistent, thespark plug heat range is too cold,or the engine has been run for longperiods of time at low speedspossibly with an incorrect fuel orfuel/oil mixture. In the case ofmulti-cylinder engines, if only oneplug shows difficulties, the problemis likely to be a weak spark fromthe ignition any event, the next step is tocheck actual spark plug new plugs are available, usethem for the next test. If not, cleanthe old ones as follows: using asharp object such as the point of asafety pin or a straightened fishhook, scrape off the deposits on theinsulator that surrounds the centerelectrode.

5 Dig down between theinsulation and sidewall and removeas much carbon as possible. Now,wash out any remaining oil orcarbon particles with a nonconduc-tive solvent such as paint thinner orunmixed gasoline. Allow the plug toair dry; blow on it if , gap each plug by tappingor bending the outer electrode. Ifyou don t know what the recom-mended gap is, use " (a bankcredit card is typically .030"). Testeach plug and HV wire combinationby connecting the wire to the plugand laying the plug on the engineblock where the gap can be plug outer body needs to makeelectrical contact to the engineblock as it does when it is screwedin , turn the engine over atnormal cranking speed and watchfor a spark. If you are in bright sun,you may have to shade the plug tosee the spark.

6 If this test shows nospark or a weak spark, troubleswith the breaker points or coilinside the Magneto are and HV wireresistance/continuity testfor one-cylinder enginesThe next test checks for a continu-ous path for the spark through theHV wire and the ignition coil. Referto the electrical diagram in Figure that for a one cylinder enginethere is a direct electrical path fromthe plug cap through the HV wire,and coil to the engine block. Thiscan be checked without takingapart the Magneto as follows: Setthe multimeter into the ohms ( )function. Use the range button tomanually select the 40 k range.(Auto ranging may not work heredue the inductance of the coil).Now, touch one probe tip to theengine block and the other to themetal connector inside the plugwire cap.

7 The meter should readthe resistance of the coil and HVwire in series. Good readings willrange from 3 k to 15 k . Higherreadings mean a poor connection,which typically occurs either wherethe HV wire connects to the coil orat the other end where the HV wireconnects to the spark plug clipinside the cap. A reading of OLmeans an open circuit or break inthe electrical path. If a bad readingis indicated, double check to makesure you are making a good con-nection with both test and HV wire continuitytest for two-cylinder enginesIf you are testing a 2-Cylinder,2-Cycle engine (mixed fuel) thenperform the test as above for eachcylinder individually. Look for acorrelation between a bad reading(OL) and a fouled spark plug on thesame the engine is a 4-Cycle model(unmixed fuel) such as a Honda orOnan, the test is performed slightlydifferently as shown in Figure we will be looking for conti-nuity from one spark plug clip tothe other since there is only onesecondary coil which is notconnected to the engine block.

8 Anopen spark path will kill the sparkto both circuit repairsA break in the HV circuit can occurin several places as shown inFigure the poor connection or opencircuit occurs at the spark plug clip,you may be able to repair it withouttaking anything else apart. If theproblem is located inside the mag-neto, it will probably be necessaryto remove the II MULTIMETEROFFV300mVAAPRESSRANGEAUTORANGE TOUCH HOLD10A300mACOMV100V750V!FUSED1 SEC10203040 VPrimarySecondaryCoilBreakerPointsConden serFlywheelEngine Blockk Figure 1: HV wire resistance/continuity testFigure 2: Resistance/continuity test for 2-cylinder,4-cycle engines23 SERIES II MULTIMETEROFFV300mVAAPRESSRANGEAUTORANGE TOUCH HOLD10A300mACOMV100V750V!FUSED1 SEC10203040 VPrimarySecondaryCoilk Figure 3: Possible locations of breaks insecondary HV circuitPrimarySecondaryCoilTroubleshooti ng Outboard Motor Magneto Ignitions Fluke Corporation 3 Measure the contact resistanceas follows: place the multimeter inthe function and hold the probetips tightly together to obtain areference reading with the tipsshorted.

9 The reading should showbetween and ohms, notethe value. This is the place the probe tips onopposite sides of the point contactswhen the points are in the closedposition. The meter should nowread no more the greater thanthe reference reading. Higher read-ings indicate contamination on thecontact surfaces. If the contactsurfaces are pitted, the best choicewould be to replace the points. Ifyou can t install new ones, thencarefully clean the ones you ve object here is to remove allcontamination without damagingthe underlying preferred cleaning methodis to scrape the contact surfaceswith a sharp carpet-layer s knife,followed by a wiping with solventon a clean cloth. Filing will some-times work but there is a risk ofdamaging the underlying metalwhich will shorten the life of thecontacts.

10 In any event do not usesandpaper. The grit will imbeditself in the contact metal, render-ing the points you want a quick fix to get theengine running, try the old-timerspoint cleaning trick as follows:With the crank shaft positioned sothat the points are closed, pry thebreaker arm open and insert aclean business card between thecontact surfaces. Release thebreaker arm so that the points gripthe end of the card and then dragthe card through its width, wipingthe contacts in the process. Thecard has two properties whichmake it work. It is absorbentenough to remove oil and gentlyabrasive enough to remove you think the cleaning iscomplete, verify the results byrepeating the electrical resistancetest. Before leaving the points,make a visual inspection of the gapin the open position.