Step 5: Verify and Upgrade the Ignition System

A CJ with a fresh carb and a tired ignition system will not run well. The ignition system step
comes after the fuel system because a poorly running engine can be caused by either — and
you want to know the fuel side is honest before you start evaluating ignition.
 

The factory ignition system

Most CJs left the factory with a breaker-point ignition or an early electronic ignition depending
on year. The 1972-1974 models use a conventional point-style distributor. The 1975 and later
models use the Motorola electronic ignition system, which eliminated the points but retained the
same basic distributor design.
The Motorola electronic ignition is reasonably reliable when its components are in good
condition, but the ignition module, pickup coil, and cap and rotor all degrade with age. Check the
condition of the cap and rotor — look for carbon tracking, cracked towers, and worn rotor tip.
Check the plug wires for cracking and proper seating. Check the ignition coil for cracks and
verify it is producing adequate output.
 

HEI conversion — the most commonly recommended ignition upgrade

The General Motors High Energy Ignition system, most commonly sourced from a 1970s-1980s
GM V8 application, is the most frequently recommended ignition upgrade for the 258. The HEI
distributor is a self-contained unit with the ignition module built into the distributor cap, which
simplifies the wiring considerably. The module produces a stronger, more consistent spark
across a wider RPM range than the factory Motorola system, particularly at lower RPMs where
the 258 spends most of its time.
The HEI swap requires an adapter to use the GM distributor in the AMC 258 block, as the
distributor drive is different. Conversion kits are available and well-documented. The wiring
simplification alone — two wires versus the multi-wire factory harness — is worth the conversion
for a Jeep that has had previous wiring issues.

Timing

Set the timing correctly before you evaluate anything else about how the engine runs. Incorrect
timing — particularly retarded timing — causes overheating, poor fuel economy, and a general
feeling of laziness that gets misdiagnosed as a carburetor or fuel system problem. The correct
base timing for the 258 varies slightly by year and application, but 8-10 degrees before top dead
center is a common starting point. Always check your specific application.
Timing that has drifted over time is a common finding on neglected CJs. The distributor hold-
down clamp loosens, the distributor rotates slightly, and suddenly the engine that ran fine last
year feels sluggish and runs hot. Check it before you start buying parts.