My feeling - ignition.
1. The TFI coil MUST HAVE A FULL 12 VOLTS TO IT AT THE + TERMINAL. Check it while running, not with the engine off, key on. The old ignition resistance wire or resistor MUST BE BYPASSED!
Again, I just don't have words for how WRONG this is!
The MODULE must have somewhere above 10.5 volts to operate correctly.
The coil can see as little as 4.5 volts and still operate!
(not at peak efficiency, but still OPERATE just the same!)
The RESISTOR WIRE DOES NOT HAVE TO BE REMOVED!
And shouldn't be removed if you are still running a factory style Jeep/DuraSpark ignition module!
If you want to replace the Factory Jeep/DuraSpark ignition module with a 'Stealth HEI' or some other module that is capable of handling a full 12 volts with a short saturation time coil, then feel free to remove the resistor wire,
But it's not even mandatory then....
The ONLY time the resistor wire MUST be removed (Mandatory) is when you are running a CDI (Capacitive Discharge Ignition) module, and since you said NOTHING about the CDI module...
2. Check the advance - you said 10 degrees at idle - that must be with the distributor vacuum disconnected! The distributor vacuum MUST BE PORTED VACUUM - near 0 at idle, smoothly progressing as the R's are raised.
Not as bad as the last part...
You WILL find vacuum at idle with a Ford carb...
He IS correct about unplugging the vacuum advance from the distributor,
But he failed to mention you need to PLUG that vacuum line with something (like Golf 'T') while you are doing the timing....
And you DO want to use a timing light to set the timing.
Personally, I Feel that 10 degrees Initial is too much,
Should be back around 6 degrees or so,
Or even with the large cap you can fire the wrong spark plug terminal when the vacuum advance comes in...
3. Use a timing light - vacuum disconnected - it should SLOWLY advance to about the low 20's at about 2000+ RPM. That's the mechanical advance.
Actually, you should gain about 13 to 18 degrees over Initial,
Starting somewhere between 800 & 1,000 RPM,
And be all in by about 2,100 to 2,300 RPM
With your 10 degrees Initial, and a minimum of 15 degrees of CENTRIFUGAL advance,
(Everything in this distributor is 'Mechanical' so it's all 'Mechanical' advance,
Separate the three types of advance as INITIAL, CENTRIFUGAL and VACUUM)
So you are starting with about 10 degrees of INITIAL,
Then adding about 13 to 18 degrees of CENTRIFUGAL,
You should be showing about 23 to 25 degrees, and might go as high as 28 since some distributors have as much as 21 degrees advance from the factory in the Centrifugal advance head...
Here is a picture of the 'Average' AMC I-6 distributor centrifugal advance head,
And you can CLEARLY see the markings are for '18' & '21' from the centrifugal advance weights...
Some will be marked '15' & '18' on the V-8 distributors...
Some of the 'Computer Controlled' engiens will have distributors that have 'RETARDED' Timing, meaning the 'Advance' is actually different degrees of 'Retard controlled in the under hood computer...
Your advance will only show about 5 or 7 degrees of centrifugal advance,
And in that case, you will have to RE ORIENT the reluctor on the advance head shaft...
(much easier than it sounds) to make up for the computer that is no longer controlling the advance...
Then you can make the advance head limiting slots longer to get more centrifugal advance or swap out distributors for something that will work better for you...
This should be a new concept for 'Internet Experts' like Rich and the others since I haven't covered it here before and they haven't had the opportunity to plagiarize it yet,
And I haven't published a 'Tech Article' about it...
(since I didn't get paid for the last one, I probably won't)
But the last two years of CJ and all the YJ's have the 'Retarded' trigger in the distributor and need to be corrected...
4. Connect vacuum, check advance again - it should SLOWLY advance to about 35 degrees at 2800.
If in either case it "jumps" or "slams" from low to high advance - fix that.
Since there is no way to tell how much advance you have past whats on the factory scale,
This advice doesn't work very well...
The I-6 timing scales usually only show about 20 degrees, so you will have to modify something somewhere to show the entire advance curve...
Personally, I use a piece of chalk since I normally only have to do this ONCE, but you can buy balancers that have up to 90 degrees of timing marked on them,
Or you can buy a $4 timing tape that just sticks on the balancer to make the needed scale for you...
If you line your harmonic balancer 'Hash' mark up with the 0° (zero) mark on the timing scale (TDC),
Then back the balance up 10 degrees (with the balancer 'Hash' mark on the 10°),
And mark the balancer again at 0° (zero)...
Then back the balancer 'hash' mark up to the 20° indicator on the timing scale,
And mark the balancer again at the 0° mark on the scale...
You will have enough 'Scale' to complete mapping of your ignition advance properly...
Balancer 'Hash' mark... with the first made line on the 18° indicator means 18 + 10 degrees or 28 degrees...
Easy and simple once you get the hang of it and learn how the ignition/scale works.
5. Pull off a plug wire at the plug - look at the spark as it jumps to ground. It should be a scary sounding, snappy, blue/white spark at least 3/4 of an inch long. If not, find out why.
NEVER, EVER pull the plug wires off a running engine unless you know EXACTLY what you are doing.
Taking the ground away from a high voltage wire (ground is the spark plug) is a REALLY bad idea!
When you take the ground away, it's the same as jacking the spark gap open to about an inch or so,
And the coil will either discharge internally, damaging the insulation and windings (Especially with the E-core coils),
Or it will jump to ground inside the cap somewhere it's not supposed to...
MUCH better idea is to use a TEST PLUG.
You can make a test plug out of an old spark plug, and some insulated wire to ground the plug.
Strip back about 3" of insulation,
Wrap it around the threads of the plug,
Then strip about 3" of the other end of the wire, and wrap it around the battery negative terminal.
This gives you a CONTROLLED GAP to have a look at the spark in the gap,
AND you don't have to worry about grounding issues.
Electronic Ignitions should NEVER be 'Open Ground',
And I'm not crazy about those cheap spark voltage testers, since voltage is only one SMALL part of Spark Energy...
You should be more concerned with AMPERAGE, The 'Heat' the spark has,
And the DURATION, the amount of time the spark exists in the plug gap.
VOLTAGE only ionizes the spark gap,
And driving voltages up with large gaps only robs the Spark Energy Discharge of AMPERAGE & DURATION.
I could go on, but it's pointless since the 'Issue' stands out like a sore thumb!...