How High Is Too High?

[tunahead72 2,340]

We're talkin' Kohler K-series ignition coils here...

 

My '81 C-105 sits covered in an open-sided barn in Virginia most of its life, and mows about 3 acres of yard a dozen or so times a year when it's not sleeping.  It ran early last December, and then I put it to bed for the winter.  And then COVID-19 happened, and I didn't get back there to put it back to work until about a month ago.  I went through my usual preparations, cleaning out mouse nests, checking fluids, airing up the tires, greasing everything in sight, and installing a freshly charged battery.  I went to start it, it took forever, but I got it running, a little rough, but it ran for 10-15 minutes or so.  It was then lunch time, so I shut it off, came back later, and could not get it to start for more than a few seconds at a time, and that was difficult.

 

I checked for fuel, was getting a decent spurt out of the fuel pump.  I checked for spark, just by laying the connected plug on top of the head while it cranked, and had what I thought was decent spark.

 

Thinking that it had a fuel problem, I decided to bring it back home to Pennsylvania and redo the entire fuel system, which I just finished a couple of days ago.  And when I tried to start it, it cranked but would not start.  I'm still getting spurts from the fuel pump.  But now when I check for spark, I get nothing.

 

I tested the coil, primary resistance (between the + and - terminals) is about 3.5 ohms, which seems fine.  Secondary resistance (between the + terminal and the tower) is about 13,700 ohms.  That seems high to me, compared to what I usually get from a working coil on my Wheel Horses (maybe 11,00-12,000 ohms).  So my main question here -- does that necessarily indicate a bad coil, or should I be looking elsewhere for the problem?

 

The battery is reasonably strong, reading about 12.5 volts right now.  Points and condenser are about a year old, cleaned and checked the points gap yesterday and it's about .018".  Tried two different spark plug wires, both no more than a couple of years old and test okay.  Fresh spark plug, gapped to .035".

 

I do have 12 volts to the + terminal on the coil with the ignition switch in the RUN position.  I cleaned the connections there, and the battery terminals are clean, but I haven't removed and cleaned any of the other connections yet -- is it possible they're part of the problem, even though the engine is actually cranking?

 

I have a spare (new) set of points and a condenser I can put on if necessary, but I don't want to just throw parts at it without knowing what the problem is.  And I could also substitute the coil from my 310-8 (which runs, and tests OK), but I hesitate to do that because one of the terminals on that coil is slightly stripped, and it's always a challenge to get the connectors on there tight enough.

 

Any thoughts and ideas are welcome.  My trailer is waiting patiently for a load to carry back to Virginia.

 

[oldredrider 2,547]

The C-105 has a cradle mount engine. Have you checked the ground on that mount. Seen bad ones cause similar problems.

 

[tunahead72 2,340]

Not yet, but I'm going out in a bit to start checking grounds.  That kind of answers one of my questions, which is, can a bad ground anywhere cause a no-start problem like I'm having?  Sounds like the answer is YES.

 

[ebinmaine 63,113]

Bad ground can and will cause all kinds of fun things. 

 

I run extra grounds on the rigs I rewire. 

[WHX?? 46,739]

Just thinknin out loud here Tuna any chance the carb float is stuck closed? 

[squonk 38,916]

Coils rarely go bad in my experience. Just got the heck of it, pop your points cover off and run a dollar bill between your points contacts 

[tunahead72 2,340]

37 minutes ago, ebinmaine said:

Bad ground can and will cause all kinds of fun things. 

 

I run extra grounds on the rigs I rewire. 

 

Part of my brain knows that, just haven't exercised that section in a while.  I'm seeing a vague image of a wooden plaque of some sort that reinforces those ideas. 

 

18 minutes ago, WHX24 said:

Just thinknin out loud here Tuna any chance the carb float is stuck closed? 

 

Possibly, but unlikely.  I cleaned the carb very thoroughly, and replaced the needle and the seat, and the float pin.  The float seemed fine, although I did have to change the float height a bit, it was pretty far off.  Also, I think I'm getting fuel into the combustion area, I see a thin layer of fuel (I hope) under the spark plug when I remove it.

 

1 minute ago, squonk said:

Coils rarely go bad in my experience. Just got the heck of it, pop your points cover off and run a dollar bill between your points contacts 

 

Done, no change.  And it's good to know coils don't go bad very often, but I think this one is original, so 39 years old.  Nothing obvious wrong with it physically, but that secondary resistance is on the high side, just haven't seen any specs on whether it's too high.

 

--------

 

Thanks guys, I'm off to clean grounds!

 

[SylvanLakeWH 24,129]

Had similar issue on my C105 couple years back. Yup - Ground...

 

Run new ones like @ebinmaine suggested...or redo existing... at two points: Hood (lights) and frame (engine)...

[WHX?? 46,739]

Any chance you can swap out the coil with one off another tractor? I can find no specs on reading through coils either.

 You may already have it but anything in this manual help?

07 - Engine Electrical Systems.pdf

[pacer 3,159]

Since you know the tractor WILL run - then there are really only 2 things that can be the problem ... ignition or fuel!

 

If you can lay the loose plug on the head and spin the motor and get a good clean spark then its got to be fuel related. Then if you can squirt fuel in the carb and get it to hit a few times then its a fuel prob.....

[pfrederi 17,147]

21 minutes ago, pacer said:

Since you know the tractor WILL run - then there are really only 2 things that can be the problem ... ignition or fuel!

 

If you can lay the loose plug on the head and spin the motor and get a good clean spark then its got to be fuel related. Then if you can squirt fuel in the carb and get it to hit a few times then its a fuel prob.....

 

 

Of course i have had a coiple instances with Champion plugs that that would fire on eh head but not when under compression,      

Edited August 28, 2020 by pfrederi

[AMC RULES 36,945]

Ditto, swap the old plug for a new plug.

[pacer 3,159]

7 minutes ago, pfrederi said:

not when under compression,   

I have heard of this a couple times but have never run into it myself -- and, of course this not an iron clad test, but its quick and simple and many more times than not one or the other will raise its irritating little head and say "ah hah, no spark lets see whats not working, or " its not getting fuel, lets see why"

[pfrederi 17,147]

44 minutes ago, pacer said:

I have heard of this a couple times but have never run into it myself -- and, of course this not an iron clad test, but its quick and simple and many more times than not one or the other will raise its irritating little head and say "ah hah, no spark lets see whats not working, or " its not getting fuel, lets see why"

You are correct is not common but it can send you down rabbit holes when it does occur.  The less than $5 spark plug tester at harbor freight is more than worth its money...

[tunahead72 2,340]

Well, I managed to clean both ends of the ground wire on the engine cradle, and the main ground wire from the battery to the frame, and tried to start it again, no luck, still no start and no spark.  It started raining, so I'll look at more connections later.  I'm not sure what other grounds this tractor has that I can get to, but there are some other connections that have a light coating of rust on them, I'll make sure I get those cleaned up also.

 

The hood is off the tractor for now, but how and where would I add another ground from the engine to the frame?

 

I hear what you guys are saying about the spark plug.  I did continuity tests on the plug that's in there, and it seems fine, but I'll certainly try another one to see if anything changes.  And a spark plug tester has been on my list of want-to-have tools for a while, it's probably time to just pick one up and see what happens.

 

And I'll switch the coil from my 310-8 if I have to.

 

Waiting for the rain to stop... 

 

[WHX?? 46,739]

1 hour ago, pfrederi said:

send you down rabbit holes when it does occur. 

Yep ...cause it's usually intermittent problem!  

[ebinmaine 63,113]

Just last week I had a 2 stroke trimmer with a good spark leaning on the engine. Damn thing wouldn't start. 

Changed the plug. 

 

Whammahblammo!!

Fired right up. 

 

FWIW it was an NGK plug new and old. 

 

 

[ZXT 2,394]

First thing I would've swapped is the plug as others have mentioned. I've seen more AC plugs go dead from sitting over the winter than I care to remember. 

 

Like Squonk said, coils rarely die - if they do, they break down when hot and quit working. I've never seen one die from sitting. 

 

If the engine has good enough ground to crank, it ought to have a good enough ground to fire the ignition. This may not always be true, but since you've cleaned the ground strap I'd rule out a ground issue. 

 

My guess is going to be the condenser. I've seen bad condensers that would sometimes fire the plug when checking for spark with the plug out, but wouldn't fire under compression. 

 

You can also use a screw driver to break the points and see if you have spark at that point.

[lynnmor 6,775]

A marginal plug may not fire under compression so my tester is a relatively clean plug with the gap at least 50% wider that specification.

[AMC RULES 36,945]

If you said it I missed it...how old is that battery?

[tunahead72 2,340]

1 hour ago, ZXT said:

First thing I would've swapped is the plug as others have mentioned. I've seen more AC plugs go dead from sitting over the winter than I care to remember. 

 

Like Squonk said, coils rarely die - if they do, they break down when hot and quit working. I've never seen one die from sitting. 

 

If the engine has good enough ground to crank, it ought to have a good enough ground to fire the ignition. This may not always be true, but since you've cleaned the ground strap I'd rule out a ground issue. 

 

My guess is going to be the condenser. I've seen bad condensers that would sometimes fire the plug when checking for spark with the plug out, but wouldn't fire under compression. 

 

You can also use a screw driver to break the points and see if you have spark at that point.

 

Interesting...

 

I'll try a new plug.  I'm starting to think the coil is not the problem.  I'm not quite ready to rule out a ground issue, and cleaning and tightening connections is probably a good idea anyway.  And I may try replacing the condenser because I have a new one and it's easy, but keep in mind I'm not getting spark even with the plug out.

 

And I ran across a test that @SOI mentioned a long time ago (you guys remember SOI? I do ), basically connecting a meter to the - coil terminal and checking voltage while cranking, should fluctuate between 0 and 12 volts as the points open and close, not sure how my digital meter will respond to that, but it's easy.

 

47 minutes ago, AMC RULES said:

If you said it I missed it...how old is that battery?

 

Good question, and maybe important...  The battery was new in May 2017, used for three seasons and brought inside for maintenance charging every winter,  but this year doesn't seem to take a charge as quickly and maintain it like before.  I should probably charge it fully again and do a load test on it.  The starter does seem to be laboring to try to start the engine, maybe it's dirty or maybe I just need a fresh battery.

 

--------

 

I'm also considering adding a new ground or two.  "Search" has been my friend today, I've seen two ideas from old threads that sound good... @stevasaurus suggested a wire from one of the starter mounting bolts to the tractor frame.  And @Sparky mentioned a wire from the negative battery terminal to the lifting tab on top of the engine.  Both of those ideas sound good to me, does anybody have any other suggestions?

 

[SylvanLakeWH 24,129]

While you’re adding / improving grounds, may want to add one to the hood to address the wobbly hood hinge issue our C 105’s are blessed with... keep them headlights on...

 

Here’s the thread I had on this topic and the excellent advice given at the time:

 

 

[ebinmaine 63,113]

35 minutes ago, tunahead72 said:

@stevasaurus suggested a wire from one of the starter mounting bolts to the tractor frame

When we rebuild/restore were going for reliable, not original. 

I run the main negative cable from battery to the starter mount bolt. 

Then a ground from condenser, VR mount bolt, volt gauge negative terminal. 

[953 nut 51,656]

12 hours ago, ZXT said:

My guess is going to be the condenser. I've seen bad condensers that would sometimes fire the plug when checking for spark with the plug out, but wouldn't fire under compression. 

          Remove the condenser wire from the ignition coil for testing. The ignition will work without a condenser, it is there to extend the life of the ignition points.

At the moment the points open the condenser quenches the arc across the points extending their life, the rest of the time it just sits there.

[WHX?? 46,739]

14 hours ago, ebinmaine said:

Just last week I had a 2 stroke trimmer with a good spark leaning on the engine. Damn thing wouldn't start. 

Changed the plug. 

 

Whammahblammo!!

Fired right up. 

 

FWIW it was an NGK plug new and old. 

 

 

Same thing here once EB on a weed sacker... intermittent and a pull my hair out to track down. Had good spark leaning up against the fire hole but once the plug was seated nothing.

Same thing as ZXT just mentioned on a small bore Clinton. Musta pulled that flywheel a dozen times for I figured out to move the connie out from behind and try a different one.