Starting troubles -

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post #1 of 3 Old 11-30-2011, 12:19 PM Thread Starter
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1977 CJ7 
Join Date: Mar 2011
Location: Kingston Springs
Posts: 5
Starting troubles

I have a 1977 CJ7 304 with Auto transmission. Most of the time, I can't get it to start right up. I have to "try" to start it, then let it sit with the key at the On position for approx 1 minute, THEN *sometimes* it starts.

I've seen a couple different posts saying to do some carburetor work. How do I figure out which carb I have? I've tried xrefrencing the VIN but that didn't work. And, of course, she came with no manuals or paperwork.


eayres is offline  
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post #2 of 3 Old 11-30-2011, 04:08 PM Thread Starter
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1977 CJ7 
Join Date: Mar 2011
Location: Kingston Springs
Posts: 5
I figured it out. It's a Motorcraft 2100.
eayres is offline  
post #3 of 3 Old 11-30-2011, 05:08 PM
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1973 CJ5 
Join Date: Aug 2007
Location: South West Indiana
Posts: 11,180

Sounds like you are getting fed up with that!

If it's the factory ignition, there is some bad news...

The good news is, you have an MC 2100, 2 Barrel Carb from the factory.
They are infinitely rebuildable, and most times as reliable as an anvil.
The do pretty good off road, but have issues with washboard ruts.

I suggest you have a close look at the CHOKE, make sure the choke is doing what it's supposed to do, or is completely pulled off so the carb can operate without it being in the way.

Then I would have a look at fuel flow to the carb,
You should have a fuel filter pretty easy to get to,
Take the line off, put a glass jar under it, and crank the engine 15 to 30 seconds.
If you get less than a pint (30 seconds should put you closer to a quart), you need a fuel filter, fuel pump or to clear line restrictions, something like that...


Once you have done the 'Free' stuff,
Have a look at your ignition system...

Get your self a $6 'Test Light' from the parts store, the kind with the bulb in the handle,

Take the small wires off the coil.

Hook your test light wire to the NEGATIVE battery terminal, then probe the positive battery terminal to test the light.

Turn the key switch to the 'Run' position, And probe the 'Red' wire to the coil (from the '+' terminal),
You should get a BRIGHT light.
If you don't get a bright light, then you have issues with the wiring under the dash or the firewall connections.

If you do get a 'Bright' light,
Then probe the same wire while someone cranks the engine.
Again, you should get a light, but not as bright (Starter is stealing power from ignition system).
Should be bright enough to see with no issues,
If it's real dim, or not there at all, you have issues with the ignition switch or the wiring under the dash.

Connect your test light wire to the POSITIVE battery post, probe the negative post to see if you have good connection.

Probe the 'Black' or 'Green' wire that was connected to the coil '-' post.
You should get a 'Bright' light.

Turn the key to the 'Run' position and probe again,
You should get a 'Bright' light.
If you don't get a bright light, the module isn't getting a good ground.
The module has 5 wires, 4 wires in a square plug, and one wire coming out on it's own bolted to the fender...
Check your grounds, make sure the wire isn't corroded and it's hooked up, and make sure the fender it's self is getting a good 'Ground'....

If you do get the bright light with the key switch on, then move to next...

Crank the engine, you should get a FLASHING light.
If you don't get the flashing, you have an issue with the module or distributor trigger.

These modules fail like clock work, so do the distributor 'Hall Effect' triggers...
Prestolite is REALLY BAD about burning up those triggers and modules, and the coils don't fair much better...


Does the distributor have a PLASTIC vacuum advance?
Is the ignition module a 'Gold' colored box on the passenger fender, down low and forward of the shock?

That's a PRESTOLITE ignition.
Worst excuse for an ignition ever inflicted on Jeepers...

Worse news, There isn't any upgrade or 'Quick' Fixes for the stuff that's wrong with it.

The trigger won't work with any other modules,
The module won't interchange with any other modules,
There is no upgrade cap & rotor for that piece of crap.
They were just made in such small numbers no one really wanted to deal with them, so no one makes anything for them I'm aware of...


Now, leaving the key switch 'On',
Or more precisely, in the 'Run' position, Does NOTHING for the carb.
Your carb probably still has the THERMAL choke, a rod coming up from the intake manifold, so if the engine isn't warming up, the choke isn't pulling off.

Rules out choke pull off issues right away.


Leaving the ignition switch in the 'Run' position WILL heat up the ignition coil.
I wonder if you have an internal short in the ignition coil that subsides as the coil heats up?

Here is the flip side, as the coil heats up, so does the ignition module...
So while the coil might come around to working again, the module is heating up to dangerous levels.

You aren't supposed to leave the key in the 'Run' position without the engine running,
If you do, the module and coil heat up and damage themselves over time.


Unfortunately, there is no easy way to test the module, most parts stores won't have the adapter for the module, but you can try...

I would change the coil for a start, cheap and easy.


If you decide to swap out that Prestolite piece of French Crap for an ignition system that works, you have a couple of choices, both will run about $300 when completed if you use good parts.

In your case, *I* would swap the distributor out in a heart beat,
I'd install a distributor from a '79 Jeep with 304 engine.
This will give you a distributor with the proper advance curve for your engine, and it's VERY upgradeable,
It gives a very strong trigger signal, and it's as reliable and durable as anything you can find anywhere.
Runs about $50 for a replacement/rebuild from the parts store.

Then I would get the cap adapter, cap & rotor from a '79 Ford F-150 Pickup,
Buy premium brass terminals in the cap and get the good rotor.
It will fit right on your distributor, the only thing you need to fabricate is a little folded tin tab to align the cap adapter correctly, I have pictures, it takes about 15 minutes and a soda can...

Then I would get a GOOD set of plug wires.
Something that fits the new cap terminals, and something you won't have to change for the next 10 years or so.
They run about $85 from MSD, and they are 'Cut To Fit' so they will actually fit your engine.
The set comes with the crimping tool, boots, terminal ends for the distributor cap (Plug wire ends are already connected).

Then I would throw a $20 GM style HEI module to trigger the coil.
Again, cheap, reliable, easy to install and you will reuse most of the current wiring to your Prestolite module.

If you feel like it, the icing on the cake is a Ford 'E-core' coil.
Much faster saturation, water proof, doesn't have to be mounted upright, and there are MILLIONS of them in the salvage yards on every Ford made between about '86 and late '90s and beyond.
Runs about $5 to $15 at the salvage yards for the coil, bracket, connector...

This will be as reliable as an ANVIL, powerful enough to keep your vehicle hitting on all 8 cylinders, and it's all 'Over The Counter' replacement parts from any parts store.


Your second choice would be to get a GM style HEI Clone distributor from one of the aftermarket companies.
I would stick with DUI (Davis Unified Ignitions) since the '$100-$150 E-bay units have a tendency to have serious issues...

You will have to change plug wires, your old ones won't fit with the new distributor.
I suggest you stick with MSD wires, there simply isn't any better common wires on the market.

The HEI Clone is an upgrade in your case...
Anything that works RELIABLY is an upgrade, so with these older engines that had Prestolite, it's an upgrade for the reliability factor alone...

The DUI HEI isn't as much of an upgrade as the Jeep/Motorcraft distributor listed above, but it's superior to the Prestolite.
The HEI design has issues you can't fix, where you CAN fix all the issues with the above listed transplant.

The HEI clone is EASY to install, simply plug it into the engine, put on the plug wires, hook up the old coil wire to the 'Bat' terminal, and you are off to the races.


What ever you decide, let us know and we can provide instructions, diagrams, pictures, ect. to make the job MUCH easier...
JeepHammer is offline  

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