Hot Rod Farmer: How breaker point ignition systems work.December 29, 2021
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Though there has not been a engine made for decades that uses breaker points, there are still many in use on a farm or ranch. Also, the tenet of operation is the same for a modern coil-on-plug electronic ignition system. Understanding modern ignition systems begins with an investigation of the breaker point design.
I bought my 1969 Plymouth Barracuda with dual point 340 engine in the fall of 1968 and still own it. With age and mileage, the dwell on the dual points began to move away from the specified amount to another amount that made the engine happy. I figured that when I replaced the timing chain and gears, the dwell that makes the engine happy would return to the specified amount. But it did not. Why not?
Hello! I am sorry for the delay in getting back to you. I am trying to finish up getting my sweet corn planted.
I think it is great that you owned the car since new! That is wonderful!
Due to that I feel 1,000% confident that you are an expert with setting the breaker dwell from all of those years of experience. So…I will give you some ideas as to why things may have changed.
Since dwell is the time in distributor cam rotational degrees that the points are closed and the coil is being charged, we may have to think in a different direction to find the answer.
Also, keep in mind that the ignition event will be dependent on not only what is happening in the cylinder but the other primary ignition parts.
I would check the voltage at the + terminal of the coil with the engine running. You may need to have to alter the coil saturation since either the primary resistance of the ignition coil has skewed or the same has happened to the ballast resistor.
If you have an old Chrysler shop manual look up the coil resistance and that of the ballast resistor. I believe back then the ballast was 5 ohms but it has been many years, so do not trust my specification.
You may try setting the breakers to specification, bypassing the ballast with a jumper wire, and see how the engine runs. But if the coil is the culprit that test may be inconclusive. What you would look for is the engine running better but maybe not 100% as it did years ago. That would be enough data to point you in that direction.
The other possibility is the bushing in the distributor is worn and the shaft and thus, the distributor cam is turning in a slight ellipse, skewing things.
Please let me know what you find.
Have a blessed day,
Ray Bohacz…. The hot Rod Farmer!!