How To Test a Lawn Mower Magneto Coil

[@Rein_Ciarfella]

I’ve searched for those coil specs and can’t find them. Could you please just supply one link to any specs so I have a starting point? Thanks

[@TheReal1953]

Agree.....it would be nice to Google just the right phrase that takes one to the appropriate charts. You must start with a brand like Kohler and add your engine and engine spec. Takes time and doubtful that someone rounded up all the engine manufacturers and posted a mostly complete chart.

[@barriejones15]

Sadly it's almost impossible to find the relative coil specs for small engines, online or otherwise. I guess the manufacturers just want you to spend money with their dealerships/service centres. In future, maybe I'll base my purchasing on brands that are more customer accessible.

[@steadyeddie7453]

Agree. Unless you purchase the brand specific Service manual, you will not find published specs. So unless you find a coil with a dead short or open, you have to just take a chance and purchase a new coil.

[@jackwobser8283]

What resource were you using for those specs? I can't find anything regardless of whether i research the engine number or the coil number.

[@kidritalin1]

Same here

[@stevenhayes3241]

You do a really nice video, better than most on this topic!

[@steadyeddie7453]

I wish it were as easy as you said. Unfortunately, unless you purchase a brand specific Service manual, you will not find most resistance readings published anywhere on the web. Sometimes we get lucky when we test coils and find either a dead short or open. But otherwise resistance readings will vary from coil to coil. In general, yea, primary resistance should be really low (1-5 ohms), and secondary really high (10K or more). But when you suspect weak spark or a coil on its way out it gets complicated. 10K could indicate good on one coil and bad on another. But if you know of where we can find coil specs on various makes and models we would love to know. Cheers.

[@donalburns6548]

I have a service manual for the Honda 3011H HSA riding mower. From page 19-7 the primary side resistance value is 0.7 - 0.9 ohms. The secondary side resistance value is 6.3 - 7.7 kilo-ohms. After the winter, mine is suddenly open circuit on the secondary, so I need a replacement. Exact replacements are available at about $120. There are many less expensive models available, but does anyone know of a suitable but inexpensive replacement? One needs a replacement that can operate within the constraints of the appropriate radius of the flywheel - measurable. Also the holes in the arms need to match theose on the engine. But it is impossible to know how the voltage generated in the secondary relates to the resistance of the secondary - it is a function of total turns in the secondary and the wire diameter, plus a few other geometric factors. Maybe someone with experience can help point me in the right direction to find a replacement unit that will provide an appropriate voltage pulse from the secondary while costing much less than an exact replacement. Thanks.

[@peterrolex2349]

My problem is the workshop manual on my GXV160 says to remove the spark plug cap, and read the resistance. 1) its impossible to undo this .. do you use brute force? 2) The manual does not give a resistance for the cap part. So theoretically my coil might be fine but how do I know the cap part is not faulty other than buy it?

[@josephpertee2559]

I. Not getting any spark at a.idellaced the cdi and the full magneto and brand new spark plug my blue wire from magneto. Is connected to the blue wire on the CDI in the black wire is connected to the black wire on the CDI and I have an extra wire coming from the black wire into the magneto just on a screw to ground to the motor I disconnected the kill switch from the CDI but I am still not getting any spark for some reason even though everything is brand new is there any other possibilities that I'm missing

[@stephenschweitzer3194]

Excellent video on magnetos

[@SmallEngineDIY]

Thanks!

[@claudeshull7795]

My question, I have a 17.5 horse power IC OHV engine, it will start and idle but as soon I try to throttle up to mow, it dies. New carb, cleaned the flywheel, great spark. New gas. Any idea where to start troubleshooting?

[@levylovits]

The rotor may be bad or loose

[@Dlawns01]

Where do you go to get the specs of those coils? And to order parts, I fix small engines on my free time also but don't know where to find the right parts on the web.

[@SmallEngineDIY]

If you Google the model number of the engine, or mower, you should find a few sources that show the diagrams and parts list.

[@norge696]

Most can be found online. Google the engine model #

[@Rein_Ciarfella]

norge696 I’ve done that and still can’t find any resistance specs. Please supply just one link so I have a starting point. Thanks

[@jackwobser8283]

@@Rein_Ciarfella same here, can't find any good charts at all with specs

[@Rein_Ciarfella]

Jack Wobser I messaged him a while ago. Hoping to get a response with specifics.

[@FranciscoOrtiz-d9y]

Got it i learn something new today

[@smithderf]

A resistance check is not foolproof. Ignition modules contain semiconductors. If they go bad your resistance measurements may not show this. You may get a weak spark that only shows at high RPM. Ultimately you need a good spark at pull cord speeds. A pull cord speed spark check is the best test.

[@steadyeddie7453]

Agree. So many people make coil testing out to be simple. It can be if the coil is shorted or open. But intermittent spark, or an engine the dies after warming up can be more difficult to test. And resistance reading vary so much, all we can look for is really low primary and really high secondary. Not vary accurate but it helps in the diagnostics. And we have yet to find published coil specs unless we purchased the Service manual for a specific brand.

[@neilphilip2320]

Really well explained. Thanks v much! Gotta be better than simply swearing at it and getting sweaty trying to start the b****d thing when it simply a'int gonna go!

[@williamemerson1799]

Thanks ! When you're shootin in the dark, any light helps. 👍🍻 Does anybody check resistance between primary and secondary ?

[@AGeekNamedRoss]

The primary and secondary coils aren't connected electrically (only magnetically), so they should read: open.

[@williamemerson1799]

@@AGeekNamedRoss So if they weren't checked you may not realize that they were shorted, right ?

[@lyletrate7700]

I try to go by part number,xheck paper work that came with mower

[@deborahabercrombie9461]

motor wont shut off with key primary reads 00 bad coil but it runs fine just wont shut off

[@SmallEngineDIY]

Check the ground trip wire going to the coil.

[@bobgreene2892]

Is it common for an ignition coil to work reliably, then begin to falter-- starting some times, but at other times, producing a weak spark or no spark at all? It would seem an electrical device is either ON or OFF, so the intermittent, "fading" performance of an ignition coil needs explanation. ------------------------- * Trying to follow your screen display at 1:01, the ranges do not match the correct range for my own ignition coil. So, I presume acceptable Ohm range varies considerably, by the ignition coil model.

[@johnstowers4609]

These are electronic ignition coils, and as such, they contain a resistor and two transistors (placed in a Darlington configuration). Semi-conductors are heat sensitive - so yes, their performance can degrade prior to total failure. : )

[@bobgreene2892]

@@johnstowers4609 Thanks, John-- that gradual fade describes the behavior of my heater/AC blower switch in my car, as well. The switch contains a single, large resistor on a 12v circuit.

[@johnstowers4609]

@@bobgreene2892 You're welcome. Yes, as resistors age their resistance can/will change. In your case, if the resistance goes up, the voltage drop to the heater/AC blower will go down, which will result in poor blower performance. If you suspect the resistor, test the voltage to the blower itself - against the manual specs. : )

[@steadyeddie7453]

UNfortunately, coil diagnosis isn't always as easy as people make it out to be. Simple shorts or opens are easy enough to test for, but when you suspect weak spark, or intermittent engine stalling after warm up it can get complicated. We have yet to find published coil resistance specs on the web, only is brand specific Service manuals. And although primary resistances should be very low (1-5ohms), and secondary resistances should be very high (10K or more), they can vary greatly. Coils can fail when heated up, and back to normal when cooled down. And if your coil has the transistors built in, then testing moves to a new level. So it is not as simple as it works or doesn't work.

[@bobgreene2892]

@@steadyeddie7453 That answer tells me, essentially, this component can vary in value and still be "normal". That was what I suspected about the coil, so it is gratifying to learn I was on-track. My question arose after finding my mower hard to start, after starting easily 10-15 minutes before. (no other, intervening factors present, not even a poorly-ventilated gas cap).

[@user-id8ng9eq9h]

How do I look up the specs for an outboard coil?

[@poochie1480]

Google

[@T34theAmericanheavy]

Find the model online

[@jonchezzz]

I have a Stihl chainsaw that won’t switch off Is that a mag fault

[@davidhenderson3400]

First check the Kill switch. It is more likely a bad kill switch or a bad ground on the kill switch. But it could be the coil but I am betting on the switch or switch ground.

[@whasumara73]

Thank you. I appreciate it.

[@SmallEngineDIY]

Glad it helped

[@mountainmantoo]

Ignition coil. Ignition coil. IGNITION COIL. lol. Otherwise great video 👍

[@johncollins8304]

Isn't it better just to leave it on the engine, remove the wire and try to start. If nothing happens the thing is dead __ and this can happen despite APPARENTLY good resistance figures. Mine were primary 1.2 Ohm, secondary 4.8 kOhm, and body yo cap also 4.8 kOhm; but no spark no flash in an inline tester. (Magnet and body side cleaned, proper gap.

[@swiss6253]

Don't know the ideal ohms so no way to actually do this with any confidence.

[@spiritwatters]

What if u dont have a tester

[@liljoeii6091]

Good video alright alright alright

[@SmallEngineDIY]

Alright Alright!

[@texan2560]

All right all right all right.....

[@user-hn9qg5qm3o]

Did he just squeak out a fart at 7:33 minutes or was that a cat?

[@SmallEngineDIY]

Somebody step on a duck?

[@user-hn9qg5qm3o]

@@SmallEngineDIY Hahahaha!!! You know electric spark and that don’t mix well in a closed up building

[@Sherminator895]

Easy mode, chk continuity

[@jarnosaarinen4583]

Should say how to try & test a Coil not Magneto!