Timing and carb adjust after ignition upgrade... - JeepForum.com

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post #1 of 9 Old 11-29-2011, 10:49 AM Thread Starter
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Timing and carb adjust after ignition upgrade...

So I got my ignition upgraded and the Jeep is running GREAT, but I want to dial it in and have a few questions. This is the thread to what I did, if you are curious...


My questions are...

What is the suggested idle RPM's? What are the RPM's you run at, despite what is suggested?

What is the suggested timing? What do you run your timing at, despite what is suggested?

Also, when I put the #1 cylinder at TDC, the balancer was lined up EXACTLY with the TDC mark on the timing cover. I thought that was pretty cool, but then noticed that most timing covers I see are different than the one I have on my Jeep...

Here is what mine looks like...


And most of the ones I see look like this...

I'm curious if I have the wrong timing cover on the motor or is the one for my engine, a late '71 or early '72, correct?

FYI, I haven't timed it yet, but I had to rotate the distributor counterclockwise to get it to idle at 700 and that is where I left it. The carb is set at 2 1/2 turns out on the mix screws. That was the suggested starting point and I haven't messed with it yet.

Keep in mind, it starts immediately (cold or hot) and runs great. I was just looking to fine tune the thing...

Any help, comments or suggestions would be appreciated...

The world would be a better place if being stupid hurt...
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post #2 of 9 Old 11-29-2011, 05:06 PM Thread Starter
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Anyone at least have any info on why my timing cover is different???

The world would be a better place if being stupid hurt...
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post #3 of 9 Old 11-29-2011, 10:44 PM
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You would think that with all the guys around here that argue with EVERYBODY ON EVERYTHING,
ONE of them would have been around long enough to know the difference!


I 'Normally' run 6 to 10 degrees of INITIAL advance (with the vacuum advance line removed from the carb and plugged)

'Normal' curb idle speed is around 550 to 650 RPM with a manual transmission.

You are showing the old style cover ('69 & back), with 'RETARD' shown on the cover.
Back then, they didn't have induction pickups, so it was a timing light for everything, and you needed to see when the ignition was retarded.

After the advent of inductive pick ups for 'Tune Up' machines...

(Notice the 'Ear' with the hole in it just above the TDC mark on the cover in the picture? That's for those big 'Sun' machines that used to cost THOU$AND$ and didn't do much more than a timing light, vacuum gauge...)

You dropped an inductive pickup in that hole, it rode right next to the balancer to sense when the engine was SUPPOSED to trigger,
Instead of using a timing light hunting for the 'Hash' mark on the balancer...

Doing things the NEW way gave the entire space for advance readings, and more advance was getting more power and better mileage...

What the Tune Up' machines (HUGE boxes that cost a TON of money, usually empty air space, but they looked 'Futuristic' and gave idiots what they wanted... Flashing lights and large moving dial scales...)
They were sometimes in excess of $50K, and didn't do anything you can't do with a vacuum gauge, compression gauge, timing light and a spark voltage tester...

With the exception they had an oscilloscope and could SHOW YOU what the spark voltages and spark times, recovery times, ect were on the different plugs...

Since they had a trigger signal for #1, they could display all the spark voltages, discharge times and rebound times in pretty much real time,
And they could do it super-imposed, one on top of the other so you could compare to see which, if any, were failing, taking more voltage to fire, ect.

Flashy, and most adult's first close experience with a 'Computer', which were all the rage in the early 70's.
Our first one was a $15,000 unit (that's $15K in 1970's dollars! A TON of money, and we purchased it USED!)
And they ran will over $100K for the monstrous dealership units.
Mostly what they were was cabinets for testing equipment, you wouldn't believe all the adapters, hand testers, ect. you had to have to make them work!
Most times, we just did it by hand, it was MUCH more simple and faster...

Now you just plug into the computer and variations in crank speed between cylinder firings will tell you if a cylinder is laying down, if one plug is taking more voltage to fire it, ect.

You have more 'Computing' power in a digital wrist watch than those things had, since they were analog...


Obviously, I got side tracked!

No factory timing scale is going to give you more than about 20 degrees of marked advance.
The balancer hash mark/timing tab are there for INITIAL advance settings, not for more advanced tuning of the timing curve, you needed a distributor machine for that back in the day,
Or today, you can mark the balancer up to about 90 degrees and use it to map out your advance.

They have made it VERY easy with the advent of Timing Tape you stick to the balancer, then directly read the advance off the tape at the TDC mark.
With a timing tape, timing light, vacuum gauge and tach you can map out your advance at every RPM and every vacuum signal, when added together, you have a complete picture of the timing curve if you know the RPM and vacuum... (Tach & Vacuum Gauge)

I use a hand vacuum pump to pull vacuum on the distributor to map out how much vacuum advance you get with each graduation on the vacuum gauge face, you simply pull vacuum at idle, watch the timing light to get your reading a graph it.

And I use a tach and timing light to graph the mechanical advance, as the RPM goes up, you will get advance from the distributor centrifugal advance (also called 'Mechanical Advance', the springs & weights in the distributor)...

Once you add the vacuum reading, and it's corresponding advance,
The RPM centrifugal advance,
And your Initial advance, you know what the advance is doing at any given RPM and Engine load...

Seems like 'Voodoo' when you first hear about it, but it's actually simple when you figure it out.


As for tuning the carb,
First you want to tune the idle mixture...
This is pretty easy with a vacuum gauge or a tachometer.

You simply screw in the idle mixture screws LIGHTLY (They have SOFT seats, and you don't want to jam the screw in the bores!),
Then back them out about 4 turns or so as a starting point.

You are doing this for the simple reason you don't know what some 'Dilbert' did before you got there...
And turning them in, then backing them out EVENLY gets you to a starting point...
Unless you have an exhaust gas sniffer/analyzer or a 'Rich/Lean' indicator, you DO NOT want to mis-match the screws,
If one goes in half a turn, the other MUST go in half a turn, they move TOGETHER...

Start up and warm up the engine,
When it's warm, you kick the throttle so it 'Idles', no high idle, no choke, ect.

You hook up the vacuum gauge and turn the screws TOGETHER until you reach the Highest STEADY vacuum,
It should be ROCK SOLID without the needle wavering.

If you go 'In' too far (Too 'Lean' of fuel mixture) the vacuum will start to waver,
If you are too 'Rich' (Screws too far out) you won't produce the highest vacuum reading.

The second way is to watch your tach.
Bottom out the screws, back them out about 4 turns, then move them TOGETHER.
When your RPM drops by about 500 on the tach, you are VERY close to perfect idle mixture.

Manual transmssions take lest 'Curb Idle' is a set screw on the linkage, and it's next.
Manual transmissions have lower 'Curb Idle', the idle when it's sitting there warmed up...
Since you don't have to compensate for the drag an automatic transmission will produce in gear, you can set yours around 550 to 650 with no issues at all.
I actually run mine around 500 RPM since mine fires every cylinder like a watch, I don't have to speed up the engine to compensate for missing cylinders...

Once the idle mixture and the curb idle are set, you need to start messing with the choke & high idle controls on the carb.
Depending on what carb you are running, the directions are COMPLETELY different, so let us know what carb you have and post pictures if you want some 'Point & Click' directions...

Main Jets are LAST,
This requres a couple of sets of CLEAN plugs, a plug wrench, and a stretch of road where you can run about a mile FLAT OUT without having the cops up your butt,
You will need a place to turn around at each end, And shoulders to get off on.

How you NORMALLY get a main jet reading (WITHOUT A RICH/LEAN INDICATOR), is to take your vehicle out someplace you can run the guts out of it, I mean FLAT ON THE FLOOR for somewhere between 1/4 Mile and a mile...

You stop, change plugs to some bright, white plugs,
Get in, start it up and drive it as hard as you can, hold it to the floor!
When you get to the other end, YOU PUSH IN THE CLUTCH AND SHUT THE ENGINE OFF.
This will preserve your plug reading, not contaminating it with using the engine as a 'Brake' or having idle mixture change the deposits on the plug.

Turn around (Coasting if you can) Fire the engine up and do it again.
Complete this about two or three full circles, then change your plugs,
Compare the plugs against brand new one so you have a reference...

You are looking for a LIGHT WHEAT STRAW TAN,
Not medium tan, which is what you will be looking for later when you make jet changes and drive in traffic a little while...
Not 'Brown', which is quite a bit too rich,
Not 'Black' which is WAY too rich,
Not chalk white which is WAY too lean...

Just a hint of light tan on ONE SIDE of the ceramic tip insulator.
(Fuel flame front travel will only stain ONE side of the insulator... Something a lot of guys argue)

Once you have the idle mixture, main jets about where they need to be,
Then you tune the accelerator pump shot.

The accelerator pump should shoot fuel into the carb just as soon as the linkage starts moving!
NO DELAY, you can usually adjust or bend linkage rods to make this happen,
And after YEARS of wear, there is usually wear on the linkage rods and in the 'Eyes' of the connection points.
The SOONER that pump shot hits the carb, the less 'Hesitation' or 'Bog' you will have when you take off from a dead stop under load.

You experence a 'Bog' go out and do some 'Jack Rabbit' starts...
Figure out if the 'Bog' or 'Hesitation' is happening when you first try to take off, then the engine comes to life,
Or if you take off, then it hesitates a little before gaining RPM slower than before...

If the hesitation is right up front, you pump shot isn't getting to the carb fast enough,
Look for 'Sputtering' in the fuel stream at first, like it's got bubbles to expel before the fuel gets there in volume.
Look for loose or maladjusted linkages that let the throttle blades open before the pump starts to shoot.

It takes off hard, but then hesitates or shows a decrease in pulling power, noses over/front end drops,
Start looking for a pump shot that doesn't last long enough.

Bubbles and short pump shot are usually worn pump seals or valves.
You aren't getting a full accelerator pump full to start with, so you aren't getting a full pump shot.
When there is air space at the top of the pump shot (Sputtering/bubbles) that's usually faulty valves,

While short pump shots can be bad springs, misadjusted plunger assembly/linkage, ect.
I find a LOT of pumps people have messed with, so they are half compressed before you even start the pump shot, so make sure your pump is getting full stroke with a good spring to refill the pump...

To do that, you UNLOAD the linkage, then adjust so the pump shot is just starting... You will get fuel for a MUCH longer time so you can transition over to main jets smoothly...

Some pumps have weak springs, years of getting hammered on, then the only fix is to change the spring (And on some carbs, good time to rebuild!)
Holley and MC 2100 carbs have the accelerator pump on the outside, you don't have to take the carb apart to correct/rebuild the pumps, but with Carter and Rochester, you have to take the top off the carb, so might as well CLEAN/rebuild while you are there...

Once you have the idle mixture set up correctly, the accelerator pump set up correctly, the main jets set up correctly, you should have a nice, smooth transition from idle to acceleration to main jets for cursing.

You are NEVER going to get a steady, high vacuum reading or carb tune with vacuum leaks.
Make SURE you have killed all the vacuum leaks before you try ANY of this!
Even a SMALL vacuum leak will screw things up like crazy!
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post #4 of 9 Old 11-30-2011, 02:39 AM
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The first thing I'd do is wake up that reman'd Motorcraft distributer you've got.


It's a long read, but you're probably used to that after Hammer's posts.

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post #5 of 9 Old 11-30-2011, 07:48 AM
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I wouldn't twist around on the distributor just yet...
I would get the carb working, and make sure everything else is working correctly before I did that...

The factory advance curve is usually plenty when you are tuning, trying to figure out the bogging, hesitations, burping, ect.
Once you get all that worked out,
Then squeezing out the last few degrees of advance would be LAST on the list for vehicles this old and under powered.

Make sure everything else is 'Correct', then worry about the 'Add On' stuff and the advance curve...
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post #6 of 9 Old 11-30-2011, 08:49 AM Thread Starter
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Thaks for the replies. I'm at work today and will likely be working late. I'll read and digest all of this later tonight.

JeepHammer, I will take a picture of my carb and take you up on your "point and click" offer for instructions. For the record, the carb is a '77 Quadrajet (manual choke) that I did a carb kit on about a month ago.

Just so you all know, I'm happy with how it is running now. It starts immediately. There is no knock, no bogging and it has power all the way up to 4000 RPM, which is about as high as I like to take it. The idle is just a tad high, at 700 rpm and there is little room (if any) to go down on the idle screw. So I'm thinking the idle will need to go down a tad with the timing. I'm thinking I might even need to up the idle screw, just to be able to knock it back down with the timing, just a guess... The carb's mix screws are out 2 1/2 turns, which I have heard is a starting point for the carb.

Again, it is running better than ever and seems to be pretty close. I think I got lucky. Between the carb kit and the ignition switch over, I was expecting a nightmare trying to get it running again.

I'm now just getting "greedy" and would like to dial it in as much as possible.

Thanks again for the help. If it wasn't for this forum, I'd be lost and still driving a poorly running Jeep...

I will update with some pics later tonight, but it may be late. I work late and my son has a HS basketball game tonight...

The world would be a better place if being stupid hurt...
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post #7 of 9 Old 11-30-2011, 09:44 AM
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We have 'Talkers', guys with the basic knowledge, mostly gleaned from other posts/articles, but not much hands on experience,

We have 'Tinkers', guys that dink with everything, but don't fully understand the bigger picture of what some of the changes they make have on the other parts of the vehicle/systems,

We have 'Fan Boys', because something worked for them or their friends, they think EVERYONE should do the same thing regardless of cost or aggravation, proof to the contrary or the laws of physics,

Good thing we have guys with YEARS of electrical burns, busted knuckles, and experience seeing what works best in what situation and are willing to pass that onto the rest, set the record straight, and have enough education in the subjects and general science, to explain WHY this or that works, while this or that DOESN'T work as well as some people thought...

I'm somewhere in the middle...
I know what has worked for people for the last 40 or so years, so I know a good idea when I STEAL IT!
I've never had an original thought in my life...
I just apply what I know works to whatever I'm doing at the time... It may look like a 'Rube Goldberg' contraption, but if it doesn't work, I don't post it...

What I've made a lot of were MISTAKES! I've VERY GOOD at pissing money away on things that DON'T WORK...
When that happens, I get VERY VOCAL about it!

The ignition upgrade isn't 'Magic',
The cap, rotor, and better plug wires are what Ford originally intended for the Jeep/Motorcraft/DuraSpark ignition in the first place,
Jeep's bean counters put the brakes on the good parts,
So it's up to you to use them...

Ford even cheeped out, they used ALUMINUM terminals on most vehicles, but the 'Performance' vehicles got brass terminals...
If it's good enough for the factory hot rods they have to warranty, then it's a good idea for your Jeep...


The CDI module was too advanced for the factories to wrap their heads around when it came out, so they didn't use it, and still don't use it in a lot of cases...
When they have factory performance cars, or cars that won't pass emissions standards, they switch to the CDI module instead of a single fire ignition...

If it's good enough and rugged enough for the factory vehicles, why not our Jeeps?


Brass beats aluminum for an electrical conductor every time in our situations,
Plus, brass doesn't degrade like copper/aluminum when it's hit by high voltage arcs, so it's preferred...
The new style plug wire terminals ('Spark Plug Type') are MUCH better than the old socket types on the factory Jeep caps, so its an upgrade,

And a good set of plug wires just puts the icing on the cake!

Once you get the plug firing,
Then it's time to work on fuel delivery so the firing turns into FLAME!...

These Jeeps are NOT 'Military Grade', they were designed for a demographic that WAS NOT going to beat the crap out of them, mostly run them on pavement or flat roads, so there wan't a need for severe off pitch/roll carbs...
The result is the 'Bean Counter' carb, One that would pass emissions and run on a 8% grade.
No emphasis on roll since most roads don't roll (But we do off road!) and we exceed the 8% grade on a regular basis...

Since you weren't going to 'Deep Water' swim the vehicles, there wan't a need for sealed/water tight anything...
Most vehicle testing is done in 12" of STANDING water...
I don't even shift into low range for 12" of water, and I usually hit it a much higher than the 'Recommended' speed! (That's where the fun starts!)

So a good set of wires should have seriously WATER RESISTANT boots and insulation...
Can't get that with 'Socket' cap terminals, and can't get that with cheap plug wire boots!

We bang the crap out of these vehicles, so we NEED plug wire terminals that will 'Snap' onto the cap/plug terminals... They don't bounce off that way...
Good plug wires have them, cheap ones don't.

Now, I don't have a 'Military Grade' ignition system where the distributor, plug wires, spark plugs are all encased in water tight tubes and housings.
I use air pressure to keep the water out of my distributor,
I plumb that through the vent in the cap (Which WILL let water into the distributor if you don't do anything with it),
And I use dielectric grease in the groove under the cap to seal the cap to the adapter,
I use weather strip adheasive or silicone sealer to mostly seal up the vacuum advance arm hole and seal the adapter to the distributor housing...
Along with dielectric grease in BOTH SIDES of the plug wire boots (Terminal end and wire side) I get a pretty much water tight seal on my conductors.

This lets me run the engine with the distributor under water when the air compressor is pumping air into the distributor!
The drain hole at the bottom actually blows bubbles as the engine continues to run along without a misfire!

Like I said, it's not 'Original' ideas, this stuff has all been done somewhere else at one time or another, on one gadget or another,
I just put them together to make my ignition run under water and still get the spark energy where it belongs...

Works fine, cost is low, and it's nothing special in building this stuff for yourself...
It's the DEVELOPMENT AND TESTING that counts in this situation,
It's MUCH EASIER for someone to do this once they see it done and can get instructions!

I Hope your build goes along as smooth as it has so far! Sounds like you are making real headway on keeping your old Jeep doing what you want it to do!
Remember to pat yourself on the back, YOU DID THE WORK!
The more attention to detail you show, the better every project will turn out!
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post #8 of 9 Old 11-30-2011, 05:02 PM Thread Starter
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I left work a little early and have some time before my Son's B-Ball game. I went out in the garage and took some pics of the carb. As stated earlier, it's a '77 Quadrajet and I recently did a carb kit on it...

Here is the front driver side view...


Here is the front passenger side view...


And a view from the back driver side...


I'll take JeepHammer's "point and click" directions and anything anyone else has to offer.

Let me know if something looks totally out of whack on this carb. I took it apart, did the carb kit and put it back the way I got it from the PO. Not sure if he had things hooked up right or not.

Thanks again!

The world would be a better place if being stupid hurt...
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post #9 of 9 Old 12-01-2011, 08:48 AM Thread Starter
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I figured I'd show you a pic of the carb before I cleaned it up. I think it has to be in the running for dirtiest carb that was removed from a RUNNING vehicle...


The world would be a better place if being stupid hurt...
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