How to perform a comprehensive ignition tune-up

Start by looking for problems–obvious or not. Ensure fresh spark plugs, spark plug wires and distributor cap.
Set spark plug gap to factory specifications.
Remove the points, condenser and the plates these attach to and inspect the advance mechanism. Twist the points cam to ensure it has not seized, and check that it has fairly uniform resistance throughout its operating range. If it is sloppy at the beginning of the range, suspect weak or improper springs.
Before reinstalling the points plates, check that they are parallel to each other.
Use a vacuum tool to ensure the vacuum advance is still operational.
Install the new points and condenser, setting the gap to the factory spec using a feeler gauge.
Inspect the distributor housing for cracks or other physical damage.
Reassemble and install distributor.
Find, clean and mark the timing tabs on the engine and the mark on the front balancer pulley.
Start the engine and check the dwell with a tach/dwell meter, ensuring your points are gapped properly.
Have an assistant run the engine through the meat of its operating range–usually 1000 to 4000 rpm–while checking the timing and advance with a dial-back timing light.
Set ignition timing according to factory manual by rotating distributor as necessary. If factory spec is given above idle, adjust carburetor’s idle screw as necessary. Recheck the speed several times throughout the process.
With vacuum advance still disconnected, use a dial-back timing light to check and record the timing at 500-rpm increments from 1500 to at or near redline. All cars are different, but with most classic British sports cars the timing light should show near 30 degrees before 4000 rpm. If much more or less advance than this is shown, or if it happens too soon or too late, you have distributor problems and it’s time to send the distributor off for service.
Assuming the advance curve looks okay, reconnect the vacuum advance and take the car for a test drive. Listen carefully for any pinging sounds indicating pre-ignition (easy to hear) or detonation (hard to hear).
If the car runs fine and pinging sounds aren’t heard, consider the job finished. If we heard the pinging sounds, we’d either consider a switch to higher octane fuel (if possible), or we’d start retarding the timing a degree at a time until the pinging sounds go away (which is not always possible).

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Comments

sir_mike New Reader
5/25/21 10:58 a.m.

Two things you missed especially if British car...Lucas...Cheaper rotors will give problems and coils do fail to work properly.I had an issue...motor woud stumble like carb issue but saw tach going crazy.Changed coil and problem gone.

Torqued New Reader
5/25/21 3:28 p.m.

Yes coils do fail. I had an intermittent miss in my MGA that I couldn't seem to fix. It seemed worst under load or in damp weather. (Not real common in southern California, but it happens.) Finally one dark evening I had the hood up with the engine idling and I could see the spark tracing down the coil tower. There was a tiny hairline crack in the coil tower, barely visible but enough to conduct the spark at least part of the time. A new coil eliminated the intermittent miss.

Solex
6/4/22 11:08 a.m.

Good points sir_mike. I would still add the use of an adjustable spark tester to see how good is the ignition systems performance (coil + points + voltage) and on the other hand how good is the insulation of the rotor, distributor cap and even igntition cables. The best to use was Gunson Flash Test which was showing by color scale if the igntion performance is good or if there is someting to be repaired in the system. Unfortunately Gunson Flash Test is not anymore available but with a modern adjustable spark tester you can do the same.

bosswrench New Reader
8/5/23 12:04 p.m.

One of my friends rolled his racer off the trailer, and it wouldn't start, no matter what he did and all the wiring checked out. Then someone noticed the distributor cap was missing the carbon center contact! We were 20 miles from the nearest town, it was a foreign car and it was Sunday... A temporary fix was whittled out of the carbon center from a discarded 'A' flashlight battery and saved the day for him.

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