Hey Tom, thank you for your work on these small engines, enjoy your delivery. Watched one of yours on carbs( I think?) recently. I am struggling with a leaf blower at the moment but also have a trimmer, a chainsaw, a snowblower and 2 mowers. All of these little engines run great for years but the 2 stroke ones seem to eventually get into more issues. The2 stroke blower has been shifting from issue to issue, surging (solved by carb rebuild), wierd running (partially solved by filing the new metering diaphragm tip to close to original ~0.60", came in at double that), starting and running issues especially when hot - partially solved by adjusting the carb screws, now every indication of no spark. Plugs new and old tested at 2 ohms each - ok, plug wet when trying to start( no spark?), kill wires and ignition permit switch test ok, new fuel, rebuilt carb, new fuel filter, air filter ok, etc, etc . Pulled the module and used your testing theme with my trusty Multimeter......secondary - plug wire to armature = 4.2Kohms.....slightly low but ok(?); primary - armature to kill tab = 148Kohms, plug wire to kill tab = 158Kohms. I assume the electronic stuff is hiding the 0.5 to 2.5 ohms of the primary. Awaiting delivery of a new module. Can not wait to test it. Any thoughts on the ~150Kohms readings? Keep up the excellent work, learning at Warp 9. Thanks Fred
I had my own workshop for 30 years and murphy was a constant companion so more often than not there was more than 1 problem or inconclusive. If I had a buck for every coil I tested that had good values but was crap....in the end I gave up these tests, it is only an indication ie if the coil is crap this will confirm it...or not. The most useful test (and fast) if the motor is running - but has an ignition problem - is to remove the cap from the coil and start the motor while holding (and being very careful) the end of the lead to the plug or earth if you have more than one cyl. The spark should be fat strong and blue and most importantly should easily be able to jump about 6mm. As you are holding the lead you can easily vary the distance and if the spark faulters and or the engine stops as soon as you increase the distance the slightest from the plug you know that either the coil is faulty or there is not enough power (dodgy electronics normaly wont let the engine run at all) - you have to then eliminate the plug first too of course but most often it is the coil. But if the spark and engine is still going strong with sparks an inch long you know the coil is not at fault. The next test is then the magneto coil (or with a battery ignition simply to measure the voltage at the coil - this will be pulsed if the electronics are not in the coil). Also here there is little point in measuring the resistance thru it as what makes these tests so inconclusive is a broken down insulation not bad enough to open or short it but just enough to allow moisture to get in. This then shorts it as soon as voltage builds up - same goes for the ignition coil. So you need a peak voltage meter which can be bought cheap and put in series on your multimeter. This then allows the multimeter to accurately measure the very short voltage spikes put out by the magneto and immediately shows up any problems with power supply as a high enough voltage of about 90 - 200v AC will not build up. You need to confirm those values depending on what bike/other you have as that is just from memory and I am retired now! There are also measuring charts for assessing the electronic parts but they can be hard to get right as they will vary depending on which multimeter you have. Sometimes all you can do to verify those is to employ a process of elimination. The best part of this vid was how he eliminated the TCI part of the coil from the test - well done. Hope this helps someone! All the best from Aotearoa
Excellent comments especially about the blue 6mm long spark jumping from plug to earth. You are absolutely correct. Manufacturers tell us about blue thick spark. Video author forgot air gap. If rust present it shorts magneto results in no spark. A failing plug sparks orange
@@VintageEngineRepairs The air gap clearance is a very precise measure. Any variation to the recommended would result in the spark being deteriorated. It is essential to ensure the surfaces have no rust or loose rust. I have repaired these engines for 50years.
@emanuelmifsud6754 hi, the air gap doesn’t need to be overly precise, most people use business cards to set the gap, although I don’t, I use a a specifically made gauge. You have to be quite a way off to lose spark in my experience.
A ignition issue could be as simple as a switch ! Some things you can not see completely through ! Faulty switches no doubt lead to the demise of barrels full of ignition coils and even whole machines !
I think that I have thanked you before, and if so, never mind !! Thanks Bro, I had this video saved ready for when I needed it, and today, I needed it, and now that I have actually done it, I will most likely remember it.... Thanks, again again....
Good information well delivered. Thank you Tom. I will be referencing this video again and again. I bought a box of coils at auction dirt cheap. $20 for about 20 coils, mainly Briggs Quantum and Classic types by casual observation. I will be testing them to see which are keepers.
Fantastic video. I was ready to look into buying new coils because of off readings due to my amateur mechanics. I didn't know I should chose the lowest ohm setting for primary testing and it didn't occur to me to subtract any prior ohm showing before the actual test. Thanks man.
thanks for a very well prepared and executed tutorial. Not a moment wasted! Not a single umm or errr. I learnt more than ever about this diagnosis. In my case it was a faulty ceramic resistor in the sparkplug boot. Not cracked. Looked a tiny bit discolored. Found after all the hassle of an engine pull-down for coil testing
Can you add and electronic diagram of the coil spark plug the see all the components? Maybe there is a darlington transistor inside of the coil. Who power the darligton transistor base?
Hey; every coil is different and will have different circuitry. Best is to google the specific make and model of coil and see if you can get a cutaway or a schematic for it.
Very comprehensive coverage on ignition coil testing - wish I had seen it years ago. I'm thinking I've thrown out many good ones based on faulty testing criteria. Cheers
V clear and concise. Sorry to be dim but ref to Kill Switch or Tab I assume you are referring to the 12v feed from the Ignition Switch. Your comment re removing all corrosion off the mounting plate is v useful as I have taken the coil off my Quattro and treated the base plate with KuRust to neutralise the surface rust that was on it. Before all this the car fired now there is nothing coming from the main HT lead to distributor BUT I have a 12v feed from the ignition switch. Could this KuRust treatment be stopping the earth getting back to the car body? Thanks
Yes, certainly scuff the surface once you’ve given it the rust treatment, there is often a layer of oxidation or surface contamination. Scotch brite it :)
@@VintageEngineRepairs I just did the test on my Martindale AM5 Analog MM: Primary on Rx 10 scale shows 1 ie 10 Ohms. Secondary on Rx 1K scale shows 7,5 or 7500 Ohms. I am now trying to find the specification for the coil (resistance)
If a simple coil with no electronics, I have taken a 6-volt dry cell and hooked up a ground to the armature, hooked up a spark plug, and of course, ground it. Then briefly touch the positive connection and watch the spark plug and if it has a spark, it is probably good. Just don't hold the wire on the primary just touch it like a set of points are opening and closing.
Iv got one here in FL almost lost it in 2022 it got down to 17°f with harsh humidity i was real upset ..one a few trees I got left since hurricane Michael...I got a old bench beside it and use it as shade since it came back after me cutting it almost all the way down ..they are tuff and come back strong
I know this video might be old, but I’m hoping to get an answer if possible. I just ran this test on a coil out of a snowblower and I’ve got the 1 ohms across the blade and the armature so that tested well. When I go from the armature to the end of the spark plug wire I get 10. It’s a four stroke engine and you said that should be around five so does that mean that this coil is bad? It will Faintly light, my in-line tester, but will not spark the spark plug.
@ ok thanks, still not sure why I can’t get spark on the engine then. The only thing that is plugged in on the coil is plug. We have a plug that is known to be good and have tried a second one also. I have also cleaned the flywheel and tried a .014 and .012 gap and the still the plug won’t spark.
Good, thorough video, as always but I suspect I'll have to watch it multiple times to have a grasp. In the meantime, a quick question. I recently bought an older Echo chainsaw. The seller mentioned something about the coil, so I assumed it would be a spark problem, but starts right up and runs great. The problem is that the kill switch doesn't work. In true backyard mechanic fashion, I replaced the switch which was quite loose. That didn't fix the issue. Could a faulty ignition coil cause the problem I described? Thanks
This is only a very basic test and I don't place much value on testing coils with a multimeter myself. If you are suspecting a bad coil then the surest way of testing it is replacing it with a known good coil. If problem goes away then you know the original coil was bad. The reason a multimeter test on a coil is generally not really useful is that a multimeter operates on a very low voltage whilst the coil itself generates on a high voltage. High voltage can travel through carbonized coil lacquer or jump creating partial coil shorts. The other thing that can happen is that the windings expand when the coil gets warm and if the lacquer on the copper windings of the coil is damaged this can short it, whereas when it is cold it functions normally.
7:11 Pleas, Help me out here, ok so if you get inconsistent reading o the primary coil then proceed to a more accurate testing, which is testing the secondary winding: HT lead to armature HT lead to kill tab When you said if the reading between the HT and armature are correct, but the reading between the HT and kill tab are incorrect that means the electronic components inside the coil are bad? Or just interfering and causing higher/different reading thus giving a false sign that the coil is bad? So the most trusty test is between HT lead to amature? Or both reading HT lead to armature and HT lead to kill tab have to be the same to finally say the coil is good?
I'm working on a sv720-3045 kohler. I have no crank over at all. New battery, checked the starter, which tested ok. Checked plugs, they are shot. Tested coils 1 was (P) .698, (S) 17.80, the other was (P) .734 (S) 19.85. So if I understand correctly the secondary winding on both are a bit low, correct?
One thing to note, I tested a coil on my Honda B16A2 engine. The readings were in spec but the engine wouldn't fire. I purchased a new coil after confirming the primary side trigger was switching. The engine fired up straight away after fitting the new coil. Same goes for coil on plugs on my Yamaha R6, was misfiring at 12000rpm on track, the readings were in spec both hot and cold. I bought and fitted new coils, the bike now revved through 12k and onto 15k whilst accelerating.
You’re absolutely right! You can have coils that are within spec, but the electronics that control spark timing etc can be bad and that will cause a misfire or non sparking coil :) this is just one of the tests we can do, at home, to get an idea of a good or bad coil.
Hi. I’m struggling to be confident about which are the right testing points. I know which one the spark plug lead is. I have two cables connected other than the spark plug lead. One is green and one is black. Not sure which is the kill switch lead. Can you help identify the right connection points for testing? I’m testing a coil for a 2022 Honda CRF 250R motocross bike.
Great video Tom, as ever. Out of interest, what should the resistance be between the kill tab and the HT barb? Would it be the same as either kill to armature, or barb to armature? Thanks
I got a 0.37 resistance reading for the primary and 73 resistance reading on the secondary. This is a 2 stroke engine. Seems like the primary is higher than you suggested. Is it bad?
I mention it in the video, using both the hot side tab and the armature to check secondary. One will give high the other will give normal readings. If this is the case then it’s likely just the electronics.
Is this only applicable with older units? I ask because I tested two brand new ones yesterday after watching this video. Secondary coil - 5.5k, primary coil 8.5 megaohms. After scouring the web someone said the circuitry in newer ones prevents an accurate reading of the primary.
Tom, I have been watching and re-watching your video on resistance values in small engine ignition modules, specically a 2 stroke module. The secondary measurements on my original module =4100 ohms, while the new module = 2600 ohms. The primary values original module = >30 Mohms ( fritzed?), new module = weird values depending on multimeter scale, 29.5Kohm to 201Kohm to 122 Kohm. I can not rationalize the electronic circuitry impact on the primary readings. Nether coil seems to create spark at my older plug and brand new plug. Any advice here?
Hey, did you remove all possible coating that may be on the coil armature giving you high readings? Remember that, as mentioned, the electronic circuitry on the primary side can affect the resistance readings you’re getting. Are these coils both Chinese clones? What machine is it on?
My 2003 Honda XR400R service manual doesn't use resistance testing anymore. Instead Peak Voltage specs are listed which means you need an adapter for the multimeter.
Hmmmm possibly, it can be other symptoms too though! I’d suggest it’s more likely an air leak or scored piston. Have a look as the piston skirt through the exhaust port. It should be nice and clean, no scratches or vertical scoring!
@@VintageEngineRepairs Oh geez Don't jinx me Put a new OEM carburetor on it last season & ran great Occasionally would backfire thru the carburator when shut off It has spark but its faint It doesn't make a CRACK or POP sound its just real faint These small.engines are the devil
I use to test them but found many ok till they heat up when in use . Will run when cold but dies after running for a while and won’t start (check fuel tank venting ) . Also see a mention of do magnets go bad on flywheel . Although super very rare they can lose magnetism . Just use a screw driver to test if it pulls to it is most likely fine . I have personally have never seen this so to me is a myth . Good info though for a dead coil scenario
I have the same issue,I can rev high and runs great till warms up,after about 5min starts to back fire and not hit on all cylinders then dies,till cools off,thrn can repeat
Nice video - thanks. What is the name of that beautiful red blooming tree behind you, and since it is blooming now, are you from Australia. Mike Ohio USA
Hmm sounds like either the compression release isn’t working, maybe you have a seized bearing in the stater, it could be a dirty commutator, poor connection somewhere etc
Ive just replaced a faulty coil on a 21HP B&S twin. The working coil has a secondary of about 6k Ohms, the other faulty coil has a resistance of around 3k Ohms.
Thank you! I was just watching videos about Multimeters, so I'll have to watch your video but those red flowers caught my eye first..@@VintageEngineRepairs
I have a briggs and stratton opposed twin 16.5 it ran good cut haft the lawn shut it off and would not start again tested coil says it's bad sence then I've tryed 6 coils on it and everyone of them went bad on the 3 attempt I disconnected all the wires to the motor except the starter cable still nothing have you ever heard of anything like this ?
I have an old Stihl 041 power saw with electronic Sweden ignition. there is also a German electronic ignition on some of them. And I have 3 parts saws I keep robbing electronic ignitions to keep the spark working. But one by one they fail over the years. There is a coil and it is attached to another part that picks up the magnetic signal from the flywheel. But these 2 parts are no longer available from Stihl. But all 3 coils test at around 1752 ohms which seems very high. Maybe you could test coils from an old 041 Stihl saw and show us how,,,,,,,,,,,,,,,I had to update to a 046 saw, but would like to get the 041 working again,,,,,,,,,,,,
Thank you. I’m hoping that may solve my problem. My motocross bike runs perfectly well for 15-20 min then dramatically looses power. Sounds like it’s choking
Hey :) it could very well be ignition coil. There are other electronic components like stator windings and ecu’s that can also fail. If you get hold of the service manual, you can check the resistance values of each and find if any are out of specification. Hope this helps!
multimeter test can't apply to some ignition coils which a semiconductor set in the primary winding. You test the resistance of primary which could be read like open circuit and dead, but actually it's because of its planted components.
Well I got 25.5 ohms primary and 4736 secondary on the coil I replaced. Here's weird for you. If I put the spark plug against the head I wouldn't get a spark. If I put my finger in between the sparkplug and the head I would.
Thanks mate , I,ve got an 85 year old Villiers mk10 that is giving everybody mixed up with it absolute hell , bad compression despite valves being newly lapped in & gapped , ( bore belled out ) , no spark , previously severely butchered in a failed attempt to get an obscure flywheel off etc . I,ll use your method to test the coils , & go from there . Much obliged , & I,ve clicked the buttons .
Maybe you can clarify. At 6:55 you are testing between the "kill tab" and the HT terminal. You then state "If the resistance value between the armature and the HT lead or barb is correct, but the resistance value between the kill switch or kill tab and the HT lead or the barb is incorrect, then you know that it's more than likely........" How do I know if the resistance value between the kill tab and the HT lead is incorrect?
It’s the way stihl recommends you test their older coils. The only reason they don’t on the modern ones is due to the reasons I have mentioned and there is a work around.
@@VintageEngineRepairs interesting. I observed the laminated iron pieces rust between layers . The reason the core is many layers insulated electrically is because of Eddy currents. If a pathway between the plates can move 360*degrees it quenches the magnetic field. Clean it off give it quick shot of clear lacquer and away you go. Some of the multi electrode super plugs allow too much current and can melt the winding. Thanks for taking the time to post.
You completely disregarded secondary insulation breakdown. The secondary winding can and most times look normal, but at high voltage it breaks down. A multimeter will not show you if this is an issue.
@@VintageEngineRepairs No, a shorted turn cannot be resolved by resistance measurements. A single shorted turn can make the coil non-functional. A "ring test" will detect shorted turns, but it isn't something that is easy to do without more sophisticated equipment.
Major error in this video: If there's only ONE shorted turn in either the primary or secondary windings, the DC resistance measurement will be virtually unaffected, but the coil's spark output will be reduced to near zero. An ignition coil is an inductor, not a resistor, and must be test as such. You need to measure impedance (Z), not resistance, which will vary with frequency. This is why, for most D-I-Y circumstances, substitution is usually the easiest way to go.
If you're married you can tell your wife to put her finger in the top of the spark plug and give the recoil starter a pull see what happens. You'll know if it has a good spark.. There's actually a spark tester you can buy very cheap. Sometimes a meter will show a good coil but it will have a voltage leak and arc internally or the spark is weak. Always check the distance between the coil and the flywheel. The correct distance should be the thickness of a business card. It's important to set the distance after removing a coil. While it's good to use a feeler gauge, a business card will work just fine.
If this video helped you, please consider clicking on the THANKS button above to support my channel 🙌
Hey Tom, thank you for your work on these small engines, enjoy your delivery. Watched one of yours on carbs( I think?) recently. I am struggling with a leaf blower at the moment but also have a trimmer, a chainsaw, a snowblower and 2 mowers. All of these little engines run great for years but the 2 stroke ones seem to eventually get into more issues. The2 stroke blower has been shifting from issue to issue, surging (solved by carb rebuild), wierd running (partially solved by filing the new metering diaphragm tip to close to original ~0.60", came in at double that), starting and running issues especially when hot - partially solved by adjusting the carb screws, now every indication of no spark. Plugs new and old tested at 2 ohms each - ok, plug wet when trying to start( no spark?), kill wires and ignition permit switch test ok, new fuel, rebuilt carb, new fuel filter, air filter ok, etc, etc . Pulled the module and used your testing theme with my trusty Multimeter......secondary - plug wire to armature = 4.2Kohms.....slightly low but ok(?); primary - armature to kill tab = 148Kohms, plug wire to kill tab = 158Kohms. I assume the electronic stuff is hiding the 0.5 to 2.5 ohms of the primary. Awaiting delivery of a new module. Can not wait to test it. Any thoughts on the ~150Kohms readings? Keep up the excellent work, learning at Warp 9. Thanks Fred
I like the bottle brush tree in the background.
are these numbers the same with a 6 volt and a 12 volt coil?
I had my own workshop for 30 years and murphy was a constant companion so more often than not there was more than 1 problem or inconclusive. If I had a buck for every coil I tested that had good values but was crap....in the end I gave up these tests, it is only an indication ie if the coil is crap this will confirm it...or not. The most useful test (and fast) if the motor is running - but has an ignition problem - is to remove the cap from the coil and start the motor while holding (and being very careful) the end of the lead to the plug or earth if you have more than one cyl. The spark should be fat strong and blue and most importantly should easily be able to jump about 6mm. As you are holding the lead you can easily vary the distance and if the spark faulters and or the engine stops as soon as you increase the distance the slightest from the plug you know that either the coil is faulty or there is not enough power (dodgy electronics normaly wont let the engine run at all) - you have to then eliminate the plug first too of course but most often it is the coil. But if the spark and engine is still going strong with sparks an inch long you know the coil is not at fault. The next test is then the magneto coil (or with a battery ignition simply to measure the voltage at the coil - this will be pulsed if the electronics are not in the coil). Also here there is little point in measuring the resistance thru it as what makes these tests so inconclusive is a broken down insulation not bad enough to open or short it but just enough to allow moisture to get in. This then shorts it as soon as voltage builds up - same goes for the ignition coil. So you need a peak voltage meter which can be bought cheap and put in series on your multimeter. This then allows the multimeter to accurately measure the very short voltage spikes put out by the magneto and immediately shows up any problems with power supply as a high enough voltage of about 90 - 200v AC will not build up. You need to confirm those values depending on what bike/other you have as that is just from memory and I am retired now! There are also measuring charts for assessing the electronic parts but they can be hard to get right as they will vary depending on which multimeter you have. Sometimes all you can do to verify those is to employ a process of elimination. The best part of this vid was how he eliminated the TCI part of the coil from the test - well done. Hope this helps someone! All the best from Aotearoa
Thanks for watching and sharing 👍👍
Excellent comments especially about the blue 6mm long spark jumping from plug to earth. You are absolutely correct. Manufacturers tell us about blue thick spark.
Video author forgot air gap. If rust present it shorts magneto results in no spark. A failing plug sparks orange
@emanuelmifsud6754 Hey! Thanks for watching :) Though rust doesn’t affect the magnetism, it will affect the air gap clearance.
@@VintageEngineRepairs The air gap clearance is a very precise measure. Any variation to the recommended would result in the spark being deteriorated. It is essential to ensure the surfaces have no rust or loose rust. I have repaired these engines for 50years.
@emanuelmifsud6754 hi, the air gap doesn’t need to be overly precise, most people use business cards to set the gap, although I don’t, I use a a specifically made gauge. You have to be quite a way off to lose spark in my experience.
Finally someone who knows what they are talking about !
Thanks for the kind words, glad you enjoyed it!
Thanks bud. This video is timed well because I've got a saw I believe has ignition issues. This is a big help. May God bless you and keep you.
That’s awesome, best of luck fixing your issue :)
A ignition issue could be as simple as a switch !
Some things you can not see completely through !
Faulty switches no doubt lead to the demise of barrels full of ignition coils and even whole machines !
Probably the most informative and well explained i seen.
Thanks for the kind words!
Thanks
Thank you for the super thanks Graham! Your support for the channel It’s really appreciated, I’m glad you enjoyed the video! :)
I think that I have thanked you before, and if so, never mind !! Thanks Bro, I had this video saved ready for when I needed it, and today, I needed it, and now that I have actually done it, I will most likely remember it.... Thanks, again again....
Awesome! That’s great news :) you’re welcome!
Nice video Tom! Lots of great info. I need to watch this again.
Thanks Stella! Glad you enjoyed it :)
Awesome video, great explanation on how to test the coil and where to set the meter. Thanks
Glad it helped :)
Good information well delivered. Thank you Tom. I will be referencing this video again and again. I bought a box of coils at auction dirt cheap. $20 for about 20 coils, mainly Briggs Quantum and Classic types by casual observation. I will be testing them to see which are keepers.
Amazing find!! I’m pleased for you, that’ll be handy. Glad you enjoyed the video :)
Thanks
Thank you for the super thanks! Always very appreciated ☺️
Accurately articulated with great presentation.
Thank you :)
Another great video Tom! I have been testing some Stihl coils and I was getting those weird readings. I’ll be sure to check them again.
Thanks for the kind words :) glad you found it useful!
Fantastic video. I was ready to look into buying new coils because of off readings due to my amateur mechanics. I didn't know I should chose the lowest ohm setting for primary testing and it didn't occur to me to subtract any prior ohm showing before the actual test. Thanks man.
Glad it helped! :)
thanks for a very well prepared and executed tutorial. Not a moment wasted! Not a single umm or errr. I learnt more than ever about this diagnosis. In my case it was a faulty ceramic resistor in the sparkplug boot. Not cracked. Looked a tiny bit discolored. Found after all the hassle of an engine pull-down for coil testing
Thank you for the kind words! I’m pleased you enjoyed it :) ahh yes those pesky resistors!! Good find, well done :)
@@VintageEngineRepairs have you considered US Presidential debating??😁😁😁
🤣😆 I’ll leave that to the …experts :)
Excellent video. That's more about an ignition coil I've heard from anyone. Thanks 😊
Awesome! Glad you enjoyed it :)
Can you add and electronic diagram of the coil spark plug the see all the components? Maybe there is a darlington transistor inside of the coil. Who power the darligton transistor base?
Hey; every coil is different and will have different circuitry. Best is to google the specific make and model of coil and see if you can get a cutaway or a schematic for it.
Very comprehensive coverage on ignition coil testing - wish I had seen it years ago. I'm thinking I've thrown out many good ones based on faulty testing criteria. Cheers
Thanks for watching :)
Excellent explanation, I enjoy your channel. I have replaced several ignition coils this year for customers.
Thank you! Glad you enjoyed it :)
Well done Mate!!☻
Thanks mate! Great to hear from you :)
thank you for this information - I've saved it to my favorites
Awesome! Glad you enjoyed it!
Hey, thanks so much... you had the best explanation of all the Yt's I looked. Especially needed the different values for 2 & 4 stroke coils. 👍
That’s great! Pleased to hear :) thanks!
I saved this one Tom I want to give this a try ! Not good at the electrical side of small engine repair 🤷
Awesome :)
Will tuck this one away for future reference. Thanks for all the info you provide for us.
Awesome! You’re welcome :)
V clear and concise. Sorry to be dim but ref to Kill Switch or Tab I assume you are referring to the 12v feed from the Ignition Switch. Your comment re removing all corrosion off the mounting plate is v useful as I have taken the coil off my Quattro and treated the base plate with KuRust to neutralise the surface rust that was on it. Before all this the car fired now there is nothing coming from the main HT lead to distributor BUT I have a 12v feed from the ignition switch. Could this KuRust treatment be stopping the earth getting back to the car body? Thanks
Yes, certainly scuff the surface once you’ve given it the rust treatment, there is often a layer of oxidation or surface contamination. Scotch brite it :)
@@VintageEngineRepairs OK - Thanks for the v fast reply - appreciated
@@VintageEngineRepairs I just did the test on my Martindale AM5 Analog MM: Primary on Rx 10 scale shows 1 ie 10 Ohms. Secondary on Rx 1K scale shows 7,5 or 7500 Ohms. I am now trying to find the specification for the coil (resistance)
Nice job Tom, thanks for the explanation. 👍
Thanks for watching John! :)
Anytime bud
If a simple coil with no electronics, I have taken a 6-volt dry cell and hooked up a ground to the armature, hooked up a spark plug, and of course, ground it. Then briefly touch the positive connection and watch the spark plug and if it has a spark, it is probably good. Just don't hold the wire on the primary just touch it like a set of points are opening and closing.
Yes! You can do that :)
If anyone is wondering about the tree behind him it's a wallum bottlebrush... Anyways...
Haha everyone seems to be asking me, thanks for the clarification, it’s rather dull now we’re in autumn!
Great Aussie ‘bottle brush’
Iv got one here in FL almost lost it in 2022 it got down to 17°f with harsh humidity i was real upset ..one a few trees I got left since hurricane Michael...I got a old bench beside it and use it as shade since it came back after me cutting it almost all the way down ..they are tuff and come back strong
Oh, thanks. I was wondering too. Don't have those over here in New England, USA.
I was thank you very much. That’s a beautiful tree
I know this video might be old, but I’m hoping to get an answer if possible. I just ran this test on a coil out of a snowblower and I’ve got the 1 ohms across the blade and the armature so that tested well. When I go from the armature to the end of the spark plug wire I get 10. It’s a four stroke engine and you said that should be around five so does that mean that this coil is bad? It will Faintly light, my in-line tester, but will not spark the spark plug.
Hmm I wouldn’t say so, no. 10 k-oms is still perfectly acceptable even if it fits outside the typical norms we see.
@ ok thanks, still not sure why I can’t get spark on the engine then. The only thing that is plugged in on the coil is plug. We have a plug that is known to be good and have tried a second one also. I have also cleaned the flywheel and tried a .014 and .012 gap and the still the plug won’t spark.
Very helpful! Thank you!
You’re welcome!
Good, thorough video, as always but I suspect I'll have to watch it multiple times to have a grasp. In the meantime, a quick question. I recently bought an older Echo chainsaw. The seller mentioned something about the coil, so I assumed it would be a spark problem, but starts right up and runs great. The problem is that the kill switch doesn't work. In true backyard mechanic fashion, I replaced the switch which was quite loose. That didn't fix the issue. Could a faulty ignition coil cause the problem I described? Thanks
Hmm very unlikely, it’s more likely a damaged wire mate. Get access to the coil and trace both wires to find the fault :)
Great video.
Thanks James!
What is the bush/tree/plant behind you? I would like to get one if it would grow in my area. Thank you.
I believe it’s called a bottle brush, as for it’s Latin name I don’t know I’m afraid!
This is only a very basic test and I don't place much value on testing coils with a multimeter myself.
If you are suspecting a bad coil then the surest way of testing it is replacing it with a known good coil. If problem goes away then you know the original coil was bad.
The reason a multimeter test on a coil is generally not really useful is that a multimeter operates on a very low voltage whilst the coil itself generates on a high voltage.
High voltage can travel through carbonized coil lacquer or jump creating partial coil shorts. The other thing that can happen is that the windings expand when the coil gets warm and if the lacquer on the copper windings of the coil is damaged this can short it, whereas when it is cold it functions normally.
Thanks for sharing :)
@@VintageEngineRepairs You're welcome, thanks for sharing your knowledge also :)
Good explanation of HT coil
Thanks a lot
You’re welcome :)
7:11 Pleas, Help me out here, ok so if you get inconsistent reading o the primary coil then proceed to a more accurate testing, which is testing the secondary winding:
HT lead to armature
HT lead to kill tab
When you said if the reading between the HT and armature are correct, but the reading between the HT and kill tab are incorrect that means the electronic components inside the coil are bad? Or just interfering and causing higher/different reading thus giving a false sign that the coil is bad?
So the most trusty test is between HT lead to amature?
Or both reading HT lead to armature and HT lead to kill tab have to be the same to finally say the coil is good?
Just interfering with your resistance. Secondary should always be between armature / ground and Ht, rather than the kill tab and Ht.
I'm working on a sv720-3045 kohler. I have no crank over at all. New battery, checked the starter, which tested ok. Checked plugs, they are shot. Tested coils 1 was (P) .698, (S) 17.80, the other was (P) .734 (S) 19.85. So if I understand correctly the secondary winding on both are a bit low, correct?
I’m not sure what range you’re working in there it’s just a bunch of numbers you’ve shared. Double check your service manual for the range 👍
Great information Tom 👍
Thanks Nev!
One thing to note, I tested a coil on my Honda B16A2 engine. The readings were in spec but the engine wouldn't fire. I purchased a new coil after confirming the primary side trigger was switching. The engine fired up straight away after fitting the new coil.
Same goes for coil on plugs on my Yamaha R6, was misfiring at 12000rpm on track, the readings were in spec both hot and cold. I bought and fitted new coils, the bike now revved through 12k and onto 15k whilst accelerating.
You’re absolutely right! You can have coils that are within spec, but the electronics that control spark timing etc can be bad and that will cause a misfire or non sparking coil :) this is just one of the tests we can do, at home, to get an idea of a good or bad coil.
Good video, what is that plant behind you.
I’m not sure honestly! It’s so beautiful though I can’t resist using it as a back drop while it’s in flower :)
@@VintageEngineRepairs It's a Callistemon or common name Bottle Brush.
@treecycle4631 thank you :)
Hi. I’m struggling to be confident about which are the right testing points. I know which one the spark plug lead is. I have two cables connected other than the spark plug lead. One is green and one is black. Not sure which is the kill switch lead. Can you help identify the right connection points for testing?
I’m testing a coil for a 2022 Honda CRF 250R motocross bike.
I’d suggest downloading or getting a paper copy of a workshop manual, they’ll tell you step by step the process and readings :)
Great video Tom, as ever. Out of interest, what should the resistance be between the kill tab and the HT barb? Would it be the same as either kill to armature, or barb to armature? Thanks
I got a 0.37 resistance reading for the primary and 73 resistance reading on the secondary. This is a 2 stroke engine. Seems like the primary is higher than you suggested. Is it bad?
Hmm 0.37 ohms? If so then that’s perfect! 73 ohms on secondary? That is an issue.
@@VintageEngineRepairs ya 73 and im seeing no spark when turn the motor. so the 73 means 73,000 when it should be 10000 or less? okay thanks
Well how do I know if the primary winding is bad or its internal electronics then if a high resistance could mean either is the case?
I mention it in the video, using both the hot side tab and the armature to check secondary. One will give high the other will give normal readings. If this is the case then it’s likely just the electronics.
Great video! Well explained and to the point!
Thank you :)
Is this only applicable with older units? I ask because I tested two brand new ones yesterday after watching this video. Secondary coil - 5.5k, primary coil 8.5 megaohms. After scouring the web someone said the circuitry in newer ones prevents an accurate reading of the primary.
It can do! Every coil is different, test both sides, check everything mentioned. Still no spark, replace coil.
Tom, I have been watching and re-watching your video on resistance values in small engine ignition modules, specically a 2 stroke module. The secondary measurements on my original module =4100 ohms, while the new module = 2600 ohms. The primary values original module = >30 Mohms ( fritzed?), new module = weird values depending on multimeter scale, 29.5Kohm to 201Kohm to 122 Kohm. I can not rationalize the electronic circuitry impact on the primary readings. Nether coil seems to create spark at my older plug and brand new plug. Any advice here?
Hey, did you remove all possible coating that may be on the coil armature giving you high readings? Remember that, as mentioned, the electronic circuitry on the primary side can affect the resistance readings you’re getting. Are these coils both Chinese clones? What machine is it on?
Thanks for the tip on testing coils ..iv got a lot of machines..week or no spart
Awesome :) you’re welcome!
My 2003 Honda XR400R service manual doesn't use resistance testing anymore. Instead Peak Voltage specs are listed which means you need an adapter for the multimeter.
Thanks for sharing 👍
Good video, good should help people
Thanks Bill!
the best video out there...coils suck.
Thanks :)
Hello Mate Will the cause the engine to start idle then when you raise the RPM it dies or hesitates then runs Hard to start when hot
Hmmmm possibly, it can be other symptoms too though! I’d suggest it’s more likely an air leak or scored piston. Have a look as the piston skirt through the exhaust port. It should be nice and clean, no scratches or vertical scoring!
@@VintageEngineRepairs Oh geez Don't jinx me Put a new OEM carburetor on it last season & ran great Occasionally would backfire thru the carburator when shut off It has spark but its faint It doesn't make a CRACK or POP sound its just real faint These small.engines are the devil
Great video, very informative
Thanks Al!!
I am getting .389 on the primary is that close enough to .5 ?
Yeah that’s fine!
I use to test them but found many ok till they heat up when in use . Will run when cold but dies after running for a while and won’t start (check fuel tank venting ) . Also see a mention of do magnets go bad on flywheel . Although super very rare they can lose magnetism . Just use a screw driver to test if it pulls to it is most likely fine . I have personally have never seen this so to me is a myth . Good info though for a dead coil scenario
Yep spot on re magnetism loss! Thanks for watching :)
I have the same issue,I can rev high and runs great till warms up,after about 5min starts to back fire and not hit on all cylinders then dies,till cools off,thrn can repeat
@@juliodjtakeovervelez7182 that sounds like a coil
Nice video - thanks. What is the name of that beautiful red blooming tree behind you, and since it is blooming now, are you from Australia. Mike Ohio USA
Hey! Yes it’s summer in Australia right now :) I’m here, yes! It’s a bottle brush tree, isn’t it stunning! I couldn’t resist it as a backdrop:)
Our push mower starts using recoil pull cord but not electric start. Replaced battery and bought a used starter. Advice?
When you turn the key, do you get anything? Clicking?
@@VintageEngineRepairs no key, no clicking. Just a push button. The flywheel turns once and stops.
Hmm sounds like either the compression release isn’t working, maybe you have a seized bearing in the stater, it could be a dirty commutator, poor connection somewhere etc
Ive just replaced a faulty coil on a 21HP B&S twin. The working coil has a secondary of about 6k Ohms, the other faulty coil has a resistance of around 3k Ohms.
Quite a difference! It’s interesting to see something like that :) glad you got it sorted!
Great explanation!
Thank you!
Brilliant many thanks
You’re welcome :)
Do you know what kind of tree that is behind you? It's gorgeous!
Bottle brush :)
Thank you! I was just watching videos about Multimeters, so I'll have to watch your video but those red flowers caught my eye first..@@VintageEngineRepairs
Do the flywheel magnets go bad?
They can lose magnetism yes!
Is it possible the performance of a coil would be affected by heating up? Say after 20min of riding the bike?
Yes absolutely! When a coil is on its way out, they tend to present their issues when warm and run nicely when cold.
I have a briggs and stratton opposed twin 16.5 it ran good cut haft the lawn shut it off and would not start again tested coil says it's bad sence then I've tryed 6 coils on it and everyone of them went bad on the 3 attempt I disconnected all the wires to the motor except the starter cable still nothing have you ever heard of anything like this ?
I haven’t I’m afraid, but also I haven’t worked on one, are they genuine Briggs coils or aftermarket Chinese clones?
awesome man thank you for sharing.
You’re welcome!
I have an old Stihl 041 power saw with electronic Sweden ignition. there is also a German electronic ignition on some of them. And I have 3 parts saws I keep robbing electronic ignitions to keep the spark working. But one by one they fail over the years. There is a coil and it is attached to another part that picks up the magnetic signal from the flywheel. But these 2 parts are no longer available from Stihl. But all 3 coils test at around 1752 ohms which seems very high. Maybe you could test coils from an old 041 Stihl saw and show us how,,,,,,,,,,,,,,,I had to update to a 046 saw, but would like to get the 041 working again,,,,,,,,,,,,
Coils are generally very reliable, I believe the 041 is on points ignition isn’t it?
After watching this, I found a bad coil, now I have a running chainsaw, thank you!
You’re welcome! Stunning car in your thumb nail picture!!
Another excellent video! As you know, you can test resistor spark plug resistance too. :-)
Absolutely :) and the boots! Thanks for watching!
Superhelpful! Thanks
You’re welcome!
Thank you. I’m hoping that may solve my problem. My motocross bike runs perfectly well for 15-20 min then dramatically looses power. Sounds like it’s choking
Hey :) it could very well be ignition coil. There are other electronic components like stator windings and ecu’s that can also fail. If you get hold of the service manual, you can check the resistance values of each and find if any are out of specification. Hope this helps!
I am confused as you said test resistance and not continuity but my multimeter only has a setting for continuity.
There should be a select button. Set it to continuity then push the select button to switch between continuity and resistance.
Excellent
Thank you!
multimeter test can't apply to some ignition coils which a semiconductor set in the primary winding. You test the resistance of primary which could be read like open circuit and dead, but actually it's because of its planted components.
I bring this up and explain how to test if the semiconductor material is creating false readings 👍🏻
the best is to put out typical circuits inside of primary winding. Thank you.
Great video
Thank you :)
Love your accent mate. Similar to prof. Brian Cox 😉
🤣 thanks mate hahaha
You should also test the leads. resistence in leads ???
I did :)
Well I got 25.5 ohms primary and 4736 secondary on the coil I replaced. Here's weird for you. If I put the spark plug against the head I wouldn't get a spark. If I put my finger in between the sparkplug and the head I would.
How interesting! I have no idea about that haha. Thanks for sharing though!
How about 15 mega ohms on the primary?
Way too high
Great video cheers
Thank you!
Good video Tom. See you at work sometime buddy.
Hey Travis! Thanks mate :) much appreciated!
Buy a 500volt megger to check insulation breakdown resistance.
Thanks, I’ll look into it 👍
That won't help if you have a shorted turn in one of the windings, only if you have breakdown from one winding to the other or to the core.
Thanks mate , I,ve got an 85 year old Villiers mk10 that is giving everybody mixed up with it absolute hell , bad compression despite valves being newly lapped in & gapped , ( bore belled out ) , no spark , previously severely butchered in a failed attempt to get an obscure flywheel off etc . I,ll use your method to test the coils , & go from there . Much obliged , & I,ve clicked the buttons .
Thanks Phillip, I restored a mk10, they’re an amazing machine. Solid, reliable, strong, well built! Good luck with yours!
WoW
Glad you enjoyed it :)
I stick the wires into the mains and if I see a spark I know it was good.
Into the mains?!
You didn't state what a normal reading between the kill terminal and HT terminal should be when checking for electronics.
There isn’t one
Maybe you can clarify. At 6:55 you are testing between the "kill tab" and the HT terminal. You then state "If the resistance value between the armature and the HT lead or barb is correct, but the resistance value between the kill switch or kill tab and the HT lead or the barb is incorrect, then you know that it's more than likely........" How do I know if the resistance value between the kill tab and the HT lead is incorrect?
@@wrench71 if it’s reading in the kohms or mohms like is shown 👍
Using a tool that measures resistance by using an AC signal rather than a DC voltage. A shorted turn is not detectable using a DC voltage
It’s the way stihl recommends you test their older coils. The only reason they don’t on the modern ones is due to the reasons I have mentioned and there is a work around.
@@VintageEngineRepairs interesting. I observed the laminated iron pieces rust between layers . The reason the core is many layers insulated electrically is because of Eddy currents.
If a pathway between the plates can move 360*degrees it quenches the magnetic field.
Clean it off give it quick shot of clear lacquer and away you go.
Some of the multi electrode super plugs allow too much current and can melt the winding. Thanks for taking the time to post.
You completely disregarded secondary insulation breakdown. The secondary winding can and most times look normal, but at high voltage it breaks down. A multimeter will not show you if this is an issue.
If the insulation breaks down it will show a lower resistance value. Thanks for watching !
@@VintageEngineRepairs sorry, the insulation only breaks down at high voltage (flash over), not with the 2v applied with the meter in ohms.
Ohhh yes, ideally coils will be tested by running a high enough current through on a test stand. We can only work with what we have at home :)
@@VintageEngineRepairs
No, a shorted turn cannot be resolved by resistance measurements. A single shorted turn can make the coil non-functional.
A "ring test" will detect shorted turns, but it isn't something that is easy to do without more sophisticated equipment.
Thank you!!!
You’re welcome! I hope it helps :)
Major error in this video: If there's only ONE shorted turn in either the primary or secondary windings, the DC resistance measurement will be virtually unaffected, but the coil's spark output will be reduced to near zero. An ignition coil is an inductor, not a resistor, and must be test as such. You need to measure impedance (Z), not resistance, which will vary with frequency. This is why, for most D-I-Y circumstances, substitution is usually the easiest way to go.
One shorted turn will show an open loop.
Mine work fine until about 5 minutes then they start falling
Yeah ignition 👍🏻
What is that beautiful tree you are sitting under?
I think it’s called a bottle brush!
what kind of tree is that behind you?
Bottle brush 👍
@@VintageEngineRepairs absolutely beautiful. thanks and love your content
@justinlassiter7671 thanks for the kind words words and feedback :)
👍
Thanks!
What is that tree
Bottle brush :)
👍👍
👍🤙
Multimeters arent really accurate in the .5 ohm range. It could be a dead short and you would never know it.
It's better just to swap it out and see
Where did you hear about the accuracy?
If you're married you can tell your wife to put her finger in the top of the spark plug and give the recoil starter a pull see what happens. You'll know if it has a good spark.. There's actually a spark tester you can buy very cheap. Sometimes a meter will show a good coil but it will have a voltage leak and arc internally or the spark is weak. Always check the distance between the coil and the flywheel. The correct distance should be the thickness of a business card. It's important to set the distance after removing a coil. While it's good to use a feeler gauge, a business card will work just fine.
Ha! I try and stay out of the dog house haha
This will not test insulation breakdown.
Thanks for watching
This video is exactly why I prefer text-based information... don't have to weed through all the other garbage
Cool, go find a workshop manual rather than search a video platform.
too bad most gardening equipment is 2 stroke
Noooo that’s the best thing ;) I love 2 strokes way more haha
If you use multimeter 90% of the coils will check
Ok
It’s just one way to get an idea of the condition of them.