Lawn Boy D-400 engine. No spark problem

Redpackman

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I've got an old push mower on a magnesium base. I've got a D-400 engine on it and it's run well. I think the engine was originally a "commercial engine" but of the D-400 variety. It's been acting up lately and today it just died. The compression is good. I've just gone through the carb and it's all clean and working as it should when it was running it was going strong, but then it quit.

No spark.

I thought that it probably needed new points and condenser and was able to find some at an old hardware store that still works on mowers. I went home and installed them. Still no spark.

Coil? I tried testing the coil with a meter. The secondary (the one attached to the spark plug, which I replaced too with a brand new CJ14) has an impedance of around 3.6K ohms. But here's where I have questions. the primary circuit has about .7 ohms resistance out of circuit.

With the coil all hooked up the resistance is the same. Is that right? .7 ohms (seven tenths of one ohm). That sounds powerfully close to a short to me. I've gapped the air gap on the coil using a business card. The magnet in the fly wheel is strong!

No spark

There's no real kill switch connection on this coil. Its the mower which uses the white plastic plunger to prime the carb but it also, when turned clockwise will flip a piece of metal across to a grounding point on a wire to the condenser and short/ground it to stop the spark. I've checked and the wire from the condenser is not grounded directly to ground but it only has .7 ohms resistance, too, of course.

Any help would be appreciated. I've checked that the points are set at .20 and are clean and new. The connection between the ground, the primary wire to the coil and the connector to the points is solid and not shorted to ground, but they only show .7 ohm, again.

Any help would be appreciated!!
 

sgkent

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replace the coil. All it takes is one shorted turn to pull a transformer down. Just make sure the air gap and points gap are correct first, and no wire is grounding out. Plugs can go bad too, as can the plug wire.
 

Redpackman

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Well I re-cleaned the points though they were new, and I reset the air gap for the coil and I checked the wires for shorts and could still find none, but now I have spark. Perhaps it’s only temporary. The question I still have is this: is a .7 ohms reading in the primary coil normal?
 
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