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Case 300 Spark Issue

J

jeszv

New User
Help!
Working on my Case 300 this weekend. Removed the hood and adjusted the govenor. Did not touch anything electrical. Went to start the tractor back up and it wouldn't start. Started doing some trouble shooting and had no spark at the plugs. Pulled the wire off the coil going to the distributor and had spark and the tractor fired. So I held the coil wire about 1/2" to 1" away from the coil (so I could really see the spark shooting out of the coil) and the tractor started and ran fine, until I try to plug the wire back in to the coil. I wouldn't even get the wire close to plugged in and the tractor would die. Tried this with 2 other coils, a different coil/dist wire, and different condenser - all with the same results. All of these were used parts.

Any thoughts on what to try next?

Note - I've owned this tractor for ~3 yrs and put ~50 hrs on it. It was converted to 12v before I bought it. Never had any issues until now.

Thanks!
 
Cap and rotor Moisture or carbon track. Check all plug wires for contenuity as well, a bad one can cause cap/rotor failure. Jim
 
Voltage is a fickle thing. High enough voltage can jump to a different destination that has a lower distance gap, but a higher conductivity in lower voltage. (plug voltage may be 3 or 4000 volts at idle, and at high RPM and load, it might take 10,000. A carbon track might conduct at 2000, but have too much resistance to overcome 12,000 when the wire is pulled. Jim
 
You are not the first to observe the phenomenon.

GOOGLE "antique spark intensifier". There were lots of outfits hawking them in the "old days"... spark gaps to overcome issues in the high-tension circuit to the sparkplugs.

Check your coil high-tension wire for continuity.

If wire core it should read near zero Ohms, if "carbon core" the reading should be in the 3000 Ohms to 7000 Ohms per foot range.

If the coil wire checks out OK look at the "carbon brush" in the center terminal of the distributor cap and the tips on the rotor itself.

If those parts are OK, likely the distributor cap and/or rotor are bleeding off the spark voltage.
Click to expand...
 
Did you happen to run the tractor more then usual with
heavy choking? I would check the spark plugs to see if
they are fouled with black soot. In particular look at the
internal center porcelain cone that the electrode
comes up through. If they have black soot on them
that is conductive and the spark will ground out
through that soot coating. Spray some carb cleaner on
it and use a hand wire brush on it. Maybe do this a
couple times to each one blow it off with compressed
air. Then for a final touch take a propane torch and
heat up the electrode end focus the flame down
towards that porcelain cone. It is okay if the ground
electrode get red hot for a bit. After it cools another
short blast of carb spray and compressed air. Re-gap
and install. No one has came right out and said it but
by increasing the gap for the spark to jump causes a
greater saturation of electrons in the secondary coil
winding, in other words it raises the spark voltage
when you make it jump that gap. So in the case of the
fouled plugs, the higher voltage will jump the normal
spark gap instead of shorting down the fouled
porcelain.
 
What you describe can happen if there's a lower resistance energy shorting/discharge path (like a fouled plug or moisture) causing no fire,
but when you increase the voltage necessary to arc jump a gap LIKE WHEN YOU PLACED THE WIRE FAR AWAY she can go ahead and run.

Possibilities causing your problem could be the cap n rotor assembly (caps top carbon pickup tip, hairline crack or carbon trace or
moisture),,,,,,,,Plug wire,,,,,,,,,,Some sort of a coil problem.

I would suspect and check in order,,,,,, the cap n rotor assembly, then the coil wire or plug wires, then the coil.

John T
 
Thanks for all of the comments! It ended
up being the distributor cap. The center
electrode was burnt down about 1/8 or
more, but couldn't tell until I compared
it to the new one. The spring on the
electrode was also sticking.
Tractor runs great again!
Thanks!
 
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