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Points, Condenser, and Coil

My 1970 429 CJ came from the factory in 1970 with points, condenser, and coil ignition.  There are a bunch of disadvantages to this kind of ignition.  First, mechanical points aren't reliable at high RPM.  And if you increase the spring tension to support high RPM then you create wear in the distributor.  Second, the condenser and points can't create a hot enough spark to take full advantage of the coil.  This results in a relatively weak spark.  One way to measure the spark is to look at the recommended spark plug gap.  For most points/condenser ignitions the sparkplug gap is .025 to .030 inches.

Points Triggering Capacitive Discharge Ignition

The first improvement I made in my stock ignition was the addition of a MSD 6AL capacitive discharge ignition.  This was an immediate improvement.  It sparked much hotter and I was able to open up the sparkplug gap to .055 inches.  The engine started better and it pulled stronger at high RPM.

Fancy ignitions like my MSD 6AL also support features like RPM limits, boost retards, etc.  I had an interesting problem with my RPM limit though.  When I enabled the RPM  limit it came in hundreds of RPM early and when it came in the engine bucked like a bronco, not the "soft touch" MSD advertised.

Magnetic Induction (No Points) Triggering Capacitive Discharge Ignition

I thought the problem with my RPM limit must be the MSD RPM chips or MSD ignition itself.  The MSD tech line suggested the problem was with the points triggering the ignition.  MSD thought my points were so unreliable that they were sending lots of extra ignition signals to my MSD, preventing my MSD for correctly counting the RPM.

"Oh sure," I thought, "just another tech line pointing the finger and something else."

I was already sold on replacing the my points distributor with magnetic induction, and although I wasn't sold on MSD's story, this seemed like the right time to make the switch.  Choice one was a brand new MSD distributor for $200 or more.  The advantage to this, other than how pretty it would look under my hood, would be the ability to endlessly tweak the advance curve.  Choice two would be to modify a junk-yard Ford dura-spark to fit my application.  This is a well understood process, but getting the donor unit was a hassle for me.  I took choice three.  I spent $75 for a Pertronix Ignitor that popped into my distributor and replaced my points and condenser.  Total conversion time, 30 minutes.  (It would have been done in 15 minutes, but one of the screws holding my condenser was so tight I had to use visegrips to get it out!)  And if you use the Pertronix to trigger your MSD 6 be sure to following the wiring instructions on their web site for this application.  If you just guess using the wiring diagram that comes with the unit that doesn't show the MSD, chances are you will fry everything.

With the magnetic trigger driving my MSD unit the RPM limit worked perfectly.  It came in at exactly the right RPM and it was so smooth the only way you could tell you were at limit was the engine just didn't pull any higher.

Conclusions

If my points were bouncing enough to be confusing my MSD, then they can't have been doing a really great job of triggering my sparkplugs either, can they?

First, get rid of those points. If I had it to do all over again I wouldn't put in the MSD unit until I'd installed the Pertronix.  And for $75 I'd do it right away.

Do not pass go, do not drive another 1000 miles with those crummy old points.

Second, if you need the specific features of the MSD, e.g. the RPM limits, or you need the very best performance, then add the MSD.  Certainly the MSD sparks much hotter.  Pertronix recommends opening up the plug gap by .005 since their spark is hotter than stock.  With my MSD I was able to open up the sparkplug gap by over .025.

If your messing around with your points, please make the effort to set your timing correctly.  It isn't always right to just set the initial advance to whatever your 30-year-old shop manual says.

MSD RPM Limit Tech Note

Those expensive little chips plugged into your MSD to control  RPM limits, trigger shift lights, etc. are nothing more than simple resisters.  If you don't mind cannibalizing one for the case and contacts you can put in any 59 cent Radio Shack resister you want to achieve exactly the custom RPM limit you want.  Heck, I suppose you could even put in an adjustable potentiometer and make the limit adjustable at the twist of a knob.

The chart below shows how the MSD chip resistance determines the RPM.  Just pick the RPM limit you want across the bottom, and read the resistance you want along the side.

If you want the excel spreadsheet it is available here.

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