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Garden Tractors Discussion Forum

Re: 1970 14 hp kohler no spark

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joe csuti

11-27-2013 13:46:59
4.248.89.181



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Remove coil from eng & take with you,fri-sat check with several local mower shops to see if they have a coil tester that they can test coil with,some shops have a tester for this type coil,others don't.In the meantime if you haven't done so already,check plug lead with an ohmmeter,you might have a bad plug lead,also use a new plug for testing as old plug may be bad.

If local shop can test coil & same is bad,kohler online parts lists coil for $193 if that's any help.

One thing that confuses me in you reply,when you said you disconnected kill lead at sw,do you mean you disconnected kill lead where output from trigger module & coil join OR at ign sw itself?

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Bob

11-27-2013 21:42:21
64.255.159.192



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 Re: 1970 14 hp kohler no spark in reply to joe csuti, 11-27-2013 13:46:59  
Interesting. IS there a machine out there that can definitively test this which, as you know, has diodes, a capacitor, and probably some other electronic components in it?



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joe csuti

11-28-2013 04:05:29
4.248.73.178



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 Re: 1970 14 hp kohler no spark in reply to Bob, 11-27-2013 21:42:21  
Bob-I think you misunderstood my reply,I was speaking of coil which to my knowledge has no electronic parts in it except possibly an internal condenser as looking at diag on pg 8.4 in manual of trigger module the condenser is located down stream of kill sw & I know of no ext mounted condenser on this type of ign system & suspect condenser is internal in coil,this might also explain why manual only tells you how to check secondary of coil,but nothing about checking primary.

It's possible there are either old testers/newer testers running around out there to check trigger module operation without removing trigger from eng in addition many of newer kohler eng have smart spark system which have a pickup installed in coil,when this style coil is checked I don't know if different make/mod testers have provisions for checking pickup also when testing coil & possibly be backward looking to check trigger modules,it's been over 30 yrs since I've taken a coil to a shop to have checked so I don't really know what's out there now in the way of testers.

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Bob

11-28-2013 07:34:44
64.255.159.192



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 Re: 1970 14 hp kohler no spark in reply to joe csuti, 11-28-2013 04:05:29  
Yep, no diodes, I see, but a capacitor in series with the primary winding. I wonder what the results are when checked with a Mercotronic... can it be tested as a normal coil with that capacitor in series?



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joe csuti

11-28-2013 13:57:48
4.248.75.162



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 Re: 1970 14 hp kohler no spark in reply to Bob, 11-28-2013 07:34:44  
If the the condenser is internal in coil which I more & more suspect,it probably serves the same function as a condenser in a normal points ign setup in that when points open a spike voltage up to 3 times supply voltage is generated for a fraction of a second as magnetic field in coil is collapsing,this spike voltage is induced into secondary winding of coil & boosts hv output,in addition spike also traveles back to source(points)the condenser across the points absorbs the spike voltage & reduces voltage in coil primary to as close to zero volts as possible before the next points cycle so you get max voltage buildup in primary of coil next time points close,in addition condenser prevents point burning/drawing an arc when points open,if condenser wasn't in circuit or if condenser open/shorted voltage would stay high in coil primary & have the effect of points staying open/closed all the time & no high voltage will be generated.

As far as solid state ign,I think the condenser in series with primary of coil is there to function as a buffer to protect scr in trigger so spike voltage from coil doesn't exceed piv voltage rating of scr,it may also function as a disconnect on load side of scr as usually when you use an scr in a DC circuit circuit when the scr turns on it will stay on an act as a latching relay till source voltage or load disconnected from scr so same can turn off,I found this out the hard way many yrs ago when I added foil defroster grid to rear window of my van,instead of buying a electro-mechanical relay I used a 20A solid state sw I had on hand,I killed battery in van 3 times in 2 days & couldn't figure out why,came to find out soild state sw was staying on/latched & powering defroster grid all the time after solid state sw turned on,even though sw on dash for sw turned off,only way to turn sw off was to disconnect load/supply voltage for a second or two.

As far as checking coil with a normal coil tester designed for 12v coils I don't know,it's something that would have to be tried,with condenser in series with coil primary if condenser open tester wouldn't work on coil,if condenser shorted it may give a false indication as to condition of coil or if coil working correctly,the only way I can think of to test solid state coil is to take a know good coil & see how/if it works with tester & use that as a standard when checking other coils.

Years ago I gave a thought to building a tester for trigger module/coil,however since that time either I no longer have engines with solid state ign or converted same to point ign as solid state systems went bad,just converting is an adventure in itself.

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Bob

11-28-2013 16:03:10
64.255.159.192



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 Re: 1970 14 hp kohler no spark in reply to joe csuti, 11-28-2013 13:57:48  
Actually, I believe the capacitor in those Kohler EI coils gets charged voltage from the stator that gets rectified by diode(s) in the trigger module, and when the SCR is triggered it discharges the capacitor through the coil and makes the spark, a primitive CD ignition system.



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joe csuti

11-28-2013 19:18:21
4.248.93.89



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 Re: 1970 14 hp kohler no spark in reply to Bob, 11-28-2013 16:03:10  
You may be right,I've never put a trigger module on bench & tried to do open heart surgery on it & figure out how it works,what does strike me as strange is condenser is non polarized,I would think same would have to be polarized to operate correctly in a cd system,but I may be/am probably wrong,it just may be another one of those mysteries of life/electronics.



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Bob

11-28-2013 22:01:13
64.255.159.192



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 Re: 1970 14 hp kohler no spark in reply to joe csuti, 11-28-2013 19:18:21  
HOW do we know the capacitor that's epoxied inside the coil is NP?

I've got a bad coil lying on the back of the bench somewhere... I'll try to find it and dissect it some cold and stormy day this winter when it's too cold to do much else!



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joe csuti

11-30-2013 03:01:05
4.248.75.143



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 Re: 1970 14 hp kohler no spark in reply to Bob, 11-28-2013 22:01:13  
I'm just going by symbol used in trigger module/coil drawing,the way condenser symbol drawn would indicate a non polarized condenser as there is no pos(+)end,the symbol is the same as a symbol for a condenser used in AC circuts for motor start condensers,line filters etc which are non polarized.



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wayne huber

11-27-2013 20:18:09
50.104.12.57



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 Re: 1970 14 hp kohler no spark in reply to joe csuti, 11-27-2013 13:46:59  
unplugged the wire at the ignition switch to make sure my switch was not bad. and I did check the plug wire its good . I have a in line spark tester so I can see it flash when I get spark I have the coil with me so I can check with a few places to see if anyone has a coil tester. thanks again for your feed back!!!!



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joe csuti

11-28-2013 03:02:12
4.248.73.178



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 Re: 1970 14 hp kohler no spark in reply to wayne huber, 11-27-2013 20:18:09  
Disconnect kill lead wire at junction of trigger module/coil also & check between each end of same with an ohmmeter unless you can see length of wire completely between eng connection/ign sw,wire may be grounded due to yrs of heat,vibration & rubbing against sheetmetal or brackets on tractor,if wire grounded it will give same result as turning ign sw to off/stop position even though kill lead disconnected from ign sw.

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