40 year cold start problem...solved!
 

After giving Dads 107 some much needed love over the summer and locating a snow blower, I revisited a cold start problem that has plagued the tractor since nearly new in 1971.
It would start fine in warm temps but below 50 or so it didn't like to fire and was prone to flooding. Below 30 degrees it usually would not start at all. Cranked good but wouldn't start.
Dad always said the 107 was "cold natured" and had "always" been that way. Since it was used mainly for mowing in summer, it usually sat in the shed all winter. I always thought that those Kohler engines were "that way", and could be temperamental when cold. (I recently found that to not be true, my newly acquired 126 starts right up in the cold).
It recently got a new head gasket, points, valve adjustment, air filter and carb rebuild. It ran better than it had in years. Surely after all that work it should start in cold temps with some careful handling, Right? Wrong!
I went over to mount the snow blower last week and it wouldn't hit a lick. Just a few puffs of smoke and a lame cough now and then no matter what I did. The spark plug was soaked in short order. Dad smirked a bit and had a "told you so" look.

The spark was really wimpy and yellow. I've had much hotter sparks go from my finger tip to my car door in the winter!
Hmmm, the points are new so it has to be the coil or condenser. I've got 12+ volts to the coil when cranking...wait...no way was the coil or condenser "failing" for about 40 years!
As it turns out, one or the other was bad. My bet is the coil, but it was replaced in about 1973 for another issue and the cold start problem was still there, so...??? I had a GM condenser and an internally ballasted coil (VW I think) in my collection of NOS parts. 15 minutes to replace them and vrooommm!, it fired up It now rolls over one full revolution and takes right off, even below freezing. :)
I'll leave those parts in place and see how they do, I think they will be fine.
Temps here have been in the teens at night and 20s in the day, and Dad has been going out to the garage and starting his 107 almost every day now, just to see it start in the cold. :biggrin2:
It just boggles my mind that a part could be "failing" for that many years and not have just given up totally long ago.

Still have to get the snow blower mounted. It's an early (Danco?) blower without the quick attach brackets. I had it mounted and working when the weather was better but had to remove it again to reposition the drive pulley (Stripped set screw and siezed to the shaft). I've since bought a house, moved and got busy setting up housekeeping. Now it's cold and Dads garage has no heat. It has walls and a roof, so it could be worse, though. ;)

No better feeling than that of a task accomplished and well done--especially one that has intrigued you for 40 years! Sounds like you won't get too much seat time on it, as your description indicated that your dad would like another go at it. Glad you're having fun and sharing your experience with others, with a newly revived faith in K-series engines. Here's to more great experiences with your dad and the cubs :beerchug:

Cub Cadet 123

I've spent MANY hours of seat time on the 107 since 1970, 123. I grew up with it. :)
I'm looking forward to many more on my own 126. :biggrin2:
I'm really glad to get Dad interested in the 107 again. It was his pride and joy way back when. It got worn and tired and he set it aside for quite a while because it was "too expensive to fix up". It's fixed now for not much money, and back in action just as IH intended. I think he has realized what a quality piece of equipment he bought back in the day. That's priceless.

I'm of the opinion this is not a part that has been "failing for 40 years" but an improper component fixed to the ignition system some 40 years ago. The value of the capacitor most likely restricted the "ringing" of the ignition coil and resulted in a very short and therefore weak spark event.

The condenser does keep the points from arcing, but that is not all it does. The interaction of a proper condenser and a proper coil allows the time a spark is present between the plug electrodes to be lengthened. The spark is not just one quick spark but one extended spark event lasting a few thousandths of a second. Think of the spark as the sound of a hammer hitting a bell. The bell "rings" for a certain length of time. If you put your hand on the bell and hit it, you get a sound - a short thud. This short thud is what kept your tractor from starting properly under colder, more challenging conditions.

Good find. Keep the points clean, the carb clean and do a static timing. You will be surprised how quickly the old Kolhers will fire up.

WOW,an old Danco blower ? Im guessing its one of the BB-36 models? I know they used Danco blowers on the old farmall cubs. I think they had the best of both worlds with those,they usually had a drag blade on the rear an blower on front..

Great news! Glad you got it figured out! :beerchug:

I have the same problem with my 125. I gotta ask, do you know what specific GM model and engine your condensor is for? If I can't tell the kids at the parts store, they will just give me a blank stare.