Just a short term update.

Yesterday morning, it was raining, my mini sits outside (2 car garage is full with minis), I was curious to see if my coil replacement the day before fixed the stumble and hard start problem. This problem usually happens when there is moisture in the air. It started right up. I posted the exciting news. That evening, I wanted to go to Harbor Freight (a great store for those who don't know) which is a 45 minute trip each way. It was drizzeling, the mini ran great. Yeah.

I did look at the old coil and did not see any cracks in the bakerlite. Obviously, the bakerlite was weak because it broke apart. It was just a hunch I acted on because I just don't like buying and replacing parts that don't need to be replaced. Hope this info helps anyone that has a similar issue.

I think I've fixed the problem.  Only time will tell. It rained the night before yesterday. Yesterday morning, it was hard to start and stumbled all the time I was driving it. Because it had stopped raining and started clearing, I decided to change the coil . I had another coil in stock, but that coil did not have the same terminal configuration. On the old coil, one of the small nuts had a bit of corrosion and would not turn. Me forcing it to turn; the bakerlite just crumbled. In goes the new Lucas Sport coil. Starts immediately and the test drive was without stumble. This morning, it is raining again and would make a good test of the hard starting in moisture. It fired up right away. Like I said, only time will tell if I solved my problem.

Dan, like you said coils get old.

As far as I can see on the wiring diagram, there are only a handful of basic inputs to the ECU - there isn't even a MAP sensor on an SPi.

I'd be looking at the connectors for the air temperature sensor first.
If the ECU doesn't know it's cold, it won't "pull the choke out" by enriching the mixture and cracking open the throttle in increase the fast idle.

Did you upgrade anything during the rebuild, or is it still OEM spec ?

I would start with the high tension (spark plug) leads. When they get old, they develop tiny cracks that let the spark out.  Usually not enough to see but it drains the spark off. Spraying them with WD40 is supposed to help but that is just covering thee problem. Putting any sort of coating on wires just collects dirt, exacerbating the problem. While you are at it clean and re-gap the plugs, or put new ones in.

Next stop is the source: the dizzy if you have one. (or electronic system if you have that - suggestions are for a dizzy with points). Make sure the cap is clean and dry inside and out. Look for cracks and carbon races inside (from arcing) and look at the terminals. Yje cetnre one should be in good condition and the 4 outer ones clean and smooth. The rotor does not touch them, just passes by verly closely. The spark jumps when the ponits tell it to. This causes a minute amount of metal transfer to the cap terminals which eventually get fuzzy-looking. You can scrape them off gently, though the cap should be replaced. Make sure the high tension leads are fully inserted.

Next stop is the rotor: it has a central brass contact and a wider "foot" on the outboard end. The centre one should be clean and the outer one can be smoothed/polished gently fo good spark "exposure".  Check the plastic for any signs of cracking or carbon tracks.

Next stop is the points themselves. The two mating surfaces should be clean and shiny. Sometimes they develop a tooth on one and a corersponding crater on the other., due to spark transfer. They should be mirror-shiny.The two point surfaces should line up exactly. If they are toothed or misaligned, replace them. If you are stuck for replacement, you can straighten them and polish them. Really polish them using crocus cloth. Anything coarser won't work well, though ti might get you out of a jamb. MAke sure the electrial connections are good, ingludung the low tension 

The next component is the condenser, Not much you can do except make sure it is properly anchored to the base plate and the wire is connected to the points. Replace it if at all suspect.

Now you can set the dwell - the amount of time the points are closed building up a charge in the the condenser (AKA capacitor). Using a dwell meter, you adjust the points for the amount of rotation of the dizzy shaft that the cam does not open the points. Something lie 55 degrees out of 90 degrees for a 4-cylinder. The other way is to use feeler gauges to set the gap, with the points set on the very peak of the cam lobe. The specified gap is for a fresh, unworn cam. and is calculated according to the curvature of the cam so it lifts and holds the points open the right amount of time  (I had a neighbour who couldn't get his V8 to fire: turns out he set the gap between cam lobes - his points were always open.)

A dwell meter setting will make up for a worn cam. 

Now you can set the timing. 

If the problem continues, check the voltage at the coil with the key on. If you have a non-ballasted coil, you should see 12V coming to the coil. If it is ballasted is should be somewhere around 8 to 9 volts. On a ballasted system, when you turn the key to crank the motor, a separate wire to the coil by-passes the ballast resistor and delivers full 12V for a hotter starting spark. If that wire is broken or poorly connected, you won't get the boosted spark and starting will be more difficult. 

However coils do get tires from old age. 

An electronic system will be different, though the principles the same - a good, clean spark delivered at the right time.Some are like an electronic dizzy, so the wires, cap and rotor suggestions would apply. 

Hi All,

My SPI is not running right. when there is moisture in the air, it will not start. After a night of rain, it just cranks. How I got it started this morning after a rainy night, I was fluttering the gas pedal like a carb equipped car. It caught and sputtered to life. At this moment, I can feel it missing when driving. I know this SPI is a very simple system, but a little help would be appreciated. Could it be as simple as replacing the coil? 31 years old with 78K miles. Just replaced with rebuilt lump but put all the old SPI parts back on.

Thanks Jim