74 - 300 Ignition Troubleshooting

[upbeck]

Hello All - I think that I have a wiring/harness connection problem but I'm having trouble isolating the problem - I'm trying to disconnect the "molex-type" connectors but am having trouble figuring out how to release the latch that holds these together. Does anyone know the secret?

FYI -

The first symptom was that the sled I had a couple recent instances when the key would not turn off the motor - had to use the kill switch instead.

The second and last symptom is that between my son and I, we had it suddenly die after being run for an hour or so. Ater the first, it would start back up after sitting for about 30 minutes. The second time it died while ideling, it started right away. The third time (15 minutes later, while idleing) it died and would not even fire - no spark in either cylinder.

I'm guessing that the issue is not with the ignition systems since there are two, independent systems. I exepect that the magneto ground is broken or that somewhere between the key or kill switch a short has ocurred.

I have only had this sled for a year. It is the first electrical issue that it has had since I bought it and found welded points. I'm taking this as a cue that new wiring might be in order along with a new condenser and maybe new points. But since time and parts availability is a week away, I'm trying to salvage the weekend outdoor fun with a quick fix.

[SpitfireKing]

You would have to tear everything apart and that's no quick fix unfortunately. Your best bet is to just strip all the plastic parts off and get a real good look at all the wiring, or you could be retreiving the sled in a ditch or field and that's no fun. Sometimes it's worth giving up a week-end to have it run right for all the rest.

As for the connectors, never had an issue with the main harness, but a small flat head screwdriver or dentist pick is always your friend for those jobs. Deff. sounds like you have something warming up and loosing connection, I would check all the wires on the main sled harness first, then go to the motor. If your not finding anything there, then time to take the recoil etc. off and check the points.

Should be a wiring diagram on vintagesnow.com

[JDT]

Spit you are correct there should be a 300 wiring diagram on the site.... but there is not.

Maybe MATT can fix that????

[JDT]

Upbeck remember that the kill switch and the key switch are in parelal.
If the kill works to stop the engine but the key does not then you know that the wiring is good and the engine connector is good.
So the problem is the key switch itself.

This would also explain the thing shutting off by itself.

Next time you have no spark unplug the engine connector and see if you have spark.

[upbeck]

Thanks Todd,

I did disconnect the plug at the key switch, but the "no spark" condition still exists. I have done some visual checks of the wiring harness and wiggled things around a bit, and still no spark. I thought that disconnecting the other harness connector would be another quick check, but except for what seems to be exessive brute force, that connector is not made to come appart.

multi-tasking today: on-line taxes, on-line JD troubleshooting.

Edit: I've also used my DMM to check the AC voltage at each of the primary coils. With my son pulling on the recoil - typical readings are around 0.4 volts. I don't have anything to compare this to, but this seems too low.

[SpitfireKing]

The one between the motor and sled is most deffinately made to come apart....try a little heat from a hair dryer and some WD....and if it is disconnected it should spark if there is a wiring issue that's external.

[JDT]

If you pull the plugs out the engine will pull over faster and you may read around 1 volt on the two igniton coil wires.

And you will read around 8 volts on the lighting coil. When running without a regulator the lighting coil output may be as high as 20 volts AC.

Of course these voltages will be higher when the engine is actually running.

Also note that a DVM responds much slower than an analog meter and the reads will be less because of this.

With that said as long as you have some voltage there it should have saprk and run.

The problem may be the external coils or the grounds on these coils.

Grab the meter and check these also.

[upbeck]

Success!
I had to use channel locks to grip and pull the connectors apart. Once apart, the spark came back. I'll wait to find the source of problem. Now that I know that it's outside the motor, and with the schematic, it shouldn't be too difficult to find and fix the problem.

FYI: On one circuit, the typical reading from my DVM at the primary was 120VAC. The other side/circuit, the readings were around one volt. And yet the spark seemed to be about the same on my test plug. JDT - thanks for the insight. That high voltage reading seems like something that I should not ignore.... just not tonight. My guess is that a have a defective cap. Any thoughts?

Thanks Todd, SFK and JDT. I really appreciate the help.

Jim