Figure this one out for me.

Long story! My beloved little SC Case that I embellish so much praise upon betrayed me right before it was supposed to pull a float loaded loaded with nursing home folks in a parade.

It ended up being spark but here is the whole story and maybe you can figure out what made it do this.

Last evening I washed it for the parade. I blew out the distributor (Delco 6 volt) to dry it and blew the moisture off the wires etc. Usually this is all I need to do and I do it as normal procedure before I try to start the tractor. Went to start it and it was hesitant, cranked but wouldn't fire on the first or second time over like it usually does but it did start after six or seven times over. It ran fine, and I drove it the seven and a half miles to town that evening, picking up the people mover at the threshing show site on the way to town. I parked it by the nursing home, ready for the parade the next day, and went home. This morning it cranked but wouldn't start at first. I finally got it going but it would catch on only a couple of cylinders and speed up, then die and coast down till it was almost not turning, then catch on a couple random cylinders, speed up, die and catch and do the whole process over again. The governor was opening and closing like normal. There was very little to no smoke out the exhaust but choking would make it smoke and die. I gave up on it and pulled the float through the parade with the pickup.

Later I came back with tools and did the normal checking. Points were a little close so I gapped them, I cleaned the points, I flicked them with a screw driver to make them spark and the secondary coil wire threw at least a 3/4" spark. The dist cap which is almost new looking was clean as a whistle and dry and I couldn't see visible cracks. The carbon tip in the center is solid carbon and clean, I pried up the contact strip on the rotor for better contact. After this initial cleaning and adjusting the old girl still would run real bad IF I could get it to start at all. Then I held the coil secondary wire close to metal while I hit the starter and got a good jolt from spark coming through a crack in the wire so I knew it had THAT much spark while cranking. Then I held it with heavy insulated pliers and it did throw a very healthy spark to ground. I was out of aces so as a last resort I replaced the condenser, no change, changed the coil, no change. I checked the primary wire between the coil and distributor in case it was almost broken and just barely making contact. It was good. Oh yes, it was getting a good full flow of gas to the carb and when I opened the carb drain it flowed a good stream forever.

FINALLY after all this head scratching I pulled #1 plug wire off the plug and held it close to metal while I reached around and hit the starter. The tractor started up and purred along on three cylinders as if nothing had been wrong. No clearing it's throat or stumbling. I got a jolt and dropped the wire and the end of the wire was throwing a long spark to ground while the tractor sat there not missing a beat on the three cylinders that were firing. I put #1 wire back on and it started right up and purred like a kitten.

Now the question, why did it suddenly start and run smooth when I pulled one plug wire and held it to ground? It almost had to have been something in the dist cap because it had tremendous spark coming out of the coil. I shut it down and restarted it several times after that and it popped right off. I suspect the dist cap might be cracked but why did pulling one plug wire off straighten it out immediately just like I turned on a switch? The plug wires are not rotted but they do have some age cracks and they are solid wire. End of story. LOL

are you going to replace the plug wires? Bill

Fixerupper, I know you said the cap was
clean and looked good, but did you pop all
of the wires out of the cap and look down
into those terminals? I know that when I
sold an AC engine for my brother to a member
here, I started it the night before and the
morning before he got there to look at it.
Started right up, didn't miss a beat. Well,
we he got there, it wouldn't start at all,
not even a hit. Looked it over, no spark to
the plugs. Spark out of the coil wire
though, so I looked at the points, looked
like new. Then I happened to glance down
into the coil terminal on the top of the
cap. It was one of those caps with aluminum
contacts and it was all corroded down inside
there. So I used a drill bit to clean it
out, and another one that was crusty too.
Then it started before it could even make a
full revolution. Just an idea...

Sounds like it was arcing across a couple of wires. Moving them made enough air gap to stop it.

You checked close but there may have still been
some moisture in the distributor. I have had an old
car do that. I would dry the cap and points and it
would run like a top. As it warmed up the moisture
in the distributor steamed (for lack of a weather type
term) and condensed on the cap. After you'd shut it
off it won't start back up and you have to go through
it again. I finally parked the car for a couple of days
with the distributor cap off.

We had a 74 Chevy pickup that religiously cracked
caps. When it rained it gave you fits - the most odd
behavior. Replace the cap and you were good for a
while again. You wouldn't know trouble was brewing
until it rained.

Had an A JD that wouldn't fire, took cap off mag and wiped moisture out, blew it out with air......no go! Sprayed the cap and mag interior with WD-40, blew it out with air again and it fired right up. WD=water displacer. hope this helps......Dale

The terminals are clean but sometimes that doesn't mean they are making contact. The idea of the plug wires cross firing is a good one and I never thought of it. Thanks. It looks like I had better treat her to new cap and wires. Usually I can hold the plug wire with my bare fingers but not this one.

That is my guess. You said the coil wire jolted you through a crack, the crack is wet from the water and the crack let the distributor charge leak out onto/along another wire.

Or some other frayed wire in the deal?

And when you pulled wire #1 it no longer was touching so it wasn't shorting out through that crack?

Paul

It just didn't want to be seen paling around with a bunch of old people. HeHe
Loren

Agreed on the use of WD-40.
If you really want to see if there are high voltage issues. Start the tractor at night. Look at the wires with the lights off. If the wires or any part of the system is having problems. You will see a very interesting light display on the wires and distributor. Wish I could film it, it is really interesting to see bad wires with purple arcing leaping from wire to wire.

Easy. It's that old coot named Murphy. Alway's on parade day. Seriously though you should never wash a tractor when you just have to have it.

I have never had anything fail on me when I didn't need it.

Path of least resistance.
Possibly #1 spark plug was shorting out or has a smaller gap than the others.
Alternately the other cylinders could be experiencing high resistance due to corrosion, larger plug gap, mismatched plugs etc.
Add some moisture to the equation and a spark can jump further than you think.
Like wi11y said under the right conditions when dark you can see quite the light show.
I have seen the spark on a GM Vortec 5.7 exit the boot at the cap, travel the length of the wire externally and enter the boot at the plug end.
Run it when it is dark outside and spray water on the wires with a spray bottle, if things are degraded you will either see it or hear a snapping or hear stumbling as the spark changes direction.
Moisture in the rotor can also lead you on a wild goose chase.

Come to think of it, there was no backfiring through the exhaust nor was there kickback. When it did run it seemed to hit at random, there was no rhythm or pattern to it. It did pop back through the carb. When I pulled the air filter bowl it was full of fog and steam. I still lean toward moisture lurking in the cap but those plug wires definitely do need to go. If a plug wire was cross firing into another plug wire I would think there would be the same misfire or backfire every time the wire fired a spark. If more than one plug wire was sending spark into a neighboring wire it would still happen every time it fired. When this thing did run it would hit a couple random times then just plain die till it caught again. Anyway, new cap and wires is in order. The wires have paint on them from when I painted the tractor a good twenty years ag. Time does get away from us.

Are the plug wires copper, if so, run a continuity test.

Could one wire be too close to a second and jumping?

Always keep a new cap in stock and give that a try.

Did you pull the plugs and check them