Honda Lawn mowers have a resistance test for their coils. And it always is correct.
What type of engine is it?
As far as baking. I haven't seen that done in 30 years. Usually if it is has moisture in it it is trash. Then you need to reseal it. Hmm we used to use glyptol to seal it.Wonder if it is still made.

Reading this and other DIY forums, you'll see a lot of guys are still baking coils ..apparently with good results.

Glyptol is still being made but I've never seen it sold. They do offer a list of distributors on their site one could call to try to find it.

So, do you agree then that these few resistance check alone can confirm whether or not the coil's OK?

I've totally removed it, cleaned it up, checked for worn insulation, etc.. Using an ohmeter I got the following measurements:

• From any of the three connection points to the armature - 0 continuity
• Primary winding: very low, .9-1.5 ohms
• Secondary winding: 2,930 ohms

I also checked from the primary hot to the secondary hot expecting to get nothing (Aren't the two winding supposed to be electrically isolated using induction only?) but to my surprise I instead got almost the same (2,940 ohms) as Secondary winding.

Did I just find the problem? Does this indicate an internal short? Can anyone confirm, am I right in thinking that on a good coil (primary hot to the secondary hot), one should get infinite resistance?

I went ahead and tossed it in the oven, just for the heck of it. As everyone says, "What've I got to lose?". I'll measure again in a few hours, see if there's much of a difference and report the results here for future reference for any interested. (In the meantime, I think I'll start shoppin for a replacement.)

A scientist in the making. First thought- hats off to you for wanting to learn. Second thought- what on earth is this on? Know that coils in breaker free ignitions also have a cd or other component in order to tell the coil when to release the spark. So the part that produces the spark may be fine but it is still a no go if the cd has completely failed or has gone mad. Certain manufactures require specific meters to perform your tests also.

It's just a basic coil --with no solid state circuitry-- from a 30 year old Briggs & Stratton 3.5 HP Engine (Model 92908, Type 2055 01)

2 hours in the oven at about 200 F then sat for several hrs more, oven off (@ 100 F)

• Primary winding: about the same, very low, .9-1 ohm
• Secondary winding: slightly higher than before 3,080-3,090
• Primary hot to the secondary hot, again, the same as secondary winding: 3,080-3,090 (should this not be infinite?)

Next, to spray it with waterproofing & put it all back together or purchase and install a new coil?

Strike that last part. It occurs to me, I had been thinking in terms of step up/step down transformers in which there are 2 terminals for each winding and the windings isolated. In this case, with both windings sharing the ground, I guess, in theory, measuring from primary hot to the secondary hot is measuring the total resistance of the two coils in series. The primary being only about 1 ohm or less, in practice, this is be a negligible amount ..hence the need for the coil testers, etc.