Tecumseh 8HP No Spark

[tomdigi]

Received this mower with this engine last year. Engine Info: TVXL-195 150257C 3245A

Had no compression and rebuilt completely.

Originally had weak spark, then spark went completely away; replaced plug and coil and gapped coil to spec. Still no spark. Magnets on flywheel are strong and secure.

I have the wiring harness disconnected during all of this and have the batt. connected just to the starter motor. Still no spark. This is a VERY simple unit; I'm frustrated!

Can anyone help?

Tom DiGiovanni

 

[EngineMan]

Did you remove the kill wire from the coil when you went to start it, try it without the spark plug in to see if you have spark.

 

[tomdigi]

Kill wire is off and spark plug is out and grounded.

Is there any way to test the coil with a meter? Wondering if I got a bad coil.

Tom

 

[Rivets]

Sorry, but I have to ask a stupid question. Could you have mounted the coil upside down? It's been done before.

 

[EngineMan]

One additional test you can perform. Check the impedance (resistance) of the secondary circuit at room temperature. Hook an ohmmeter test lead to the spark plug terminal of the high-tension lead and another to the lamination stack (ground). Your resistance reading should range between 2,500 and 5,000 ohms. If infinite (no continuity), an internal open circuit exists. Replace the coil. If infinite and the engine runs, your problem is an internal break of the high tension lead, a poor attachment of the spark plug terminal or improper mating of the high tension lead to the coil. A pin within the coil body skewers the lead. If the pin does not contact the wire core, there will be no continuity. The coil will often have enough available voltage to jump the gap, so you see spark. The internal arcing that occurs within the high-tension lead will eventually create enough resistance that ignition system performance will suffer. If your resistance reading is much lower than 2,500 ohms, an internal short exists. Replace the coil.

 

[tomdigi]

No such thing as a stupid question. Used to do computer tech support; you have no idea how many times the monitor switch was off. Learned to ask the simple things. The coil is mounted with "This side out" facing me.

Thanks for the 2500-5000 ohms spec. Will check as soon as the sun comes up.

 

[tomdigi]

Checked coil. Getting 4400 ohms. I'm stumped.

Check my understanding of how this ignition system works. The rotating magnets induce voltage to coil primary and secondary generates high voltage spark. No connections to coil (other than ground thru coil mount and kill wire on tab on bottom of coil) necessary. Can't get any more simple. There's no external voltage required. There's no electronic devices inside the coil. The stator under the flywheel has nothing to do with the ignition system.

HELP!

 

[tomdigi]

Is my understanding of how this thing works correct?

 

[Rivets]

Your understanding of the basic ignition system is correct, but there are other components inside the coil itself. The section in this manual better explains the ignition system than I can. It also has a good troubleshooting procedure. Hope it helps.

http://dl.dropboxusercontent.com/u/12502267/Tecumseh/Tecumseh L-Head.pdf

 

[tomdigi]

Thanks for the link. That does make me believe I've received a bad replacement coil. Again, thanks for your help.