Primary and Secodary ignition ohms/resistance

[charliec]

Hello,

I have a Super XLAO (UT: 10045A, 1980 model year) with a Prestolite electronic ignition (94605 model). I have cleaned it up, baked it at 200 degrees for 8 hours and then installed a new spark plug wire, terminal and boot using dielectric grease and non-acid (natural/neutral cure) silicone sealant around the wire entry point to help seal out water. My goal was to test it while the saw is disassembled ( i.e.., resto in progress), as I purchased it in non-running condition.  Recently, I read an article and then watched videos about Primary and Secondary resistance testing using a multi-meter, so I tried it out.  After the unit returned to room temp (i.e., post baking) I tested it and received the following results:

Primary: 1.5 Ohms
Secondary: 5,000 Ohms

I re-tested it again the next morning and received the same output/readings (i.e., consistent results).

----------------

I read that the rule of thumb (i.e., generic range) for this type of unit should be between 0.4 - 2.0 Ohms for the Primary, and 6,000 - 10,000 for Secondary.  However, I should use the ranges stated in the User Manual for my specific model.  Well, I don't have a manual so does anyone know the Homelite Ohms range for this unit?

Is there any guide to resistance/Ohms ranges and the "life" left in the coil?  For example, if the manufacturer's recommended Secondary range is 6K - 10K and mine is 5K what does that mean ( e.g., good, bad, going bad, better than spec, etc.).  Having said that, does anyone have a "cheat sheet"/chart that shows something like stated range + 20% means it is going bad, + 40% means get a replacement soon/now, + 60% or more means dead.  The same goes for under the  recommended range ( i.e., cheat sheet) and is it better to be under than over the recommended range or are both equally bad?  In addition, is there a relationship (e.g., multiplier) of Primary to Secondary to reflect good operation/life?

I know heat build up plays a big part in coil performance (i.e., resistance) so has anyone done any temp testing?  For example, heated to 200 degrees in oven and took resistance readings.  Should the results fall within a certain percentage range over standard/normal as a way to determine if it is going bad? I just threw 200 degrees out there but if there is another temp/standard for heat testing (e.g., 175 degrees), please advise.

Sorry for all the multi-layered questions,  If you can advise on any one or all the questions, I appreciate the feedback. 

Charlie

P.S., If there are other ways to test this ignition while the saw is disassembled please advise.

[undee70ss]

There’s really no way of testing a blue Prestolite electronic ignition. Primary and Secodary ignition ohms/resistance are for ignition systems with points.

[okie]

Apr 11, 2022 1:09:45 GMT -5 undee70ss said:

There’s really no way of testing a blue Prestolite electronic ignition. Primary and Secodary ignition ohms/resistance are for ignition systems with points.

because it has electronics inside. 
Your way of testing gets the results, the electronic module on the machine test, it either works or it don't. (sometimes erratic)

You can find posts on here about doing a generic replacement or for about $60 contact Standard Magneto and see if they have a replacement. If you buy a replacement save your old core laminations, they might can be used to do a $20 magneto mod using another module if decide to go that route or if you decide to rig up a spare module.