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post #21 of (permalink) Old 07-02-2009, 10:15 AM
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I think I can answer your spark question. It takes more voltage to jump a spark in a compressed fuel-air mixture than it does in free air, so a weak spark in free air might not have enough voltage to even make a spark in a running engine. If 10% of the time it can't spark at all . . . .

As for the other factors of the spark, the mixture is very turbulent in the combustion chamber. If the spark has more duration, it comes in contact with more unburned mix, in effect starting the fire in a bunch of places as the mix blows past. That increases the likelihood that all of the fuel will be burned before the exhaust valve starts to open.

The bright blue spark shows that there is more energy there, which means that once current starts to flow across the gap it will keep flowing longer.

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post #22 of (permalink) Old 07-02-2009, 11:10 AM
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Equate it to lighting a BBQ in a strong wind - using a paper match vs. a blowtorch.
You want it all to start burning at the same time to get that peak combustion pressure at the right time.

The color - if there is any leakage - to ground or internally in the coil, the spark will appear yellow or white vs. a crisp blue. I have no idea why it changes color, but it does.

The beauty of the HEI module with the TFI coil is it packs a bigger whallup. It has more current in the spark as well as lasts longer. Conventional ignition has a burn time of about .75 milliseconds (that's the time the spark is actually jumping the plug gap exposing itself to fuel particles.) The HEI/TFI has a burn time of about 2.5 milliseconds - much longer exposure. Plus the higher amperage spark is thicker, more surface area.

Sounds like you are getting there. Fix the mechanical advance before you play with the jetting. If you can't light the mixture at the right time, then adding or subtracting fuel won't do much. An exercise in futility.

And, if you change the fuel to where it's a bit better, then you fix the advance afterward, you'll have to change the fuel again.

I'll be gone till Monday - to a place where tan lines are unheard of!
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post #23 of (permalink) Old 07-02-2009, 12:06 PM
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Originally Posted by RRich View Post
I'll be gone till Monday - to a place where tan lines are unheard of!
Ethiopia?

And so as not to completely derail your thread & to corroborate Rich's statement on the potency... I've previously ran points & TR/TFI ignitions and was "bitten" by both, not *that* bad. All I know is after recently swapping in the TBI system (which requires my old MC dizzy to signal the 7pin "HEI" [EST] module & GM TFI coil), it will light you slam up! The effect IMHO is minutely less than being tazored... same intense pain, same loss of involuntary bodily functions, same "coming to" moments later wonder WTF just happened,... just no LEO shouting to stay down

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post #24 of (permalink) Old 07-02-2009, 12:47 PM Thread Starter
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I didn't think about turbulance within each cylinder having an affect on the spark, "blowing it out". Now that part makes sense. I will definately fix my advance problem before the mixture issue, or just not complain about the very little power until i do fix it. But, let me throw a question out there. Would running the engine with a ported vac port open cause a stumble as R's increase, with no load? Maybe some more troubleshooting will answer that for me.... Thanks folks

And where are tan lines unheard of? hmm...brings up a thought...tan lines are generally caused by parts of the skin being covered up from the sun. So if those parts are not covered up......I'll leave it open from there.

'88 YJ
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post #25 of (permalink) Old 07-04-2009, 12:53 AM
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Quote:
Originally Posted by USMCYJ View Post
Anyway, I checked centrifigual advance, nothing.
No vac line connected, the wife got the 6 up to 2k and there was no advance.
Something WRONG there,
You should have had about AT LEAST 5 to 7 come in, even with the later computer versions of the distributor...

Quote:
With vac connected, it traveled, with slow R increase, fairly evenly up to I'd say 26*.

My scale ends at 24.
That sounds about correct...
Starting with 10 Initial, and adding about 15 of vacuum, you would end up with about 25 total or there abouts...

I can't imagine what is keeping the centrifugal advance from working...
Normally the centrifugal advance is bullet proof in the Ford type distributors!
GM HEI Distributors used to waste the advance weights in fairly short order, but Ford distributors chug along for ever without problems...

Quote:
I haven't had the chance to disassemble the dist to see what is sticking, disconnected or broken, but hopefully will sometime over the weekend.

An issue I came across while checking the centrifigual advance, with vac line disconnected, was right around 1500RPM. The engine would stumble.

By this time, I had set the mixture screws to achieve best mixture, using a vaccuum gauge and propane at idle. So, when the engine stumbled, I shot propane down the carb throat and it evened out.

Too lean...Idle mixture screws are are used for just that, Idle...correct me if I'm wrong please.

So my original thought was too small of jets.
First off,
Did you do the screw the idle mixture screws 'IN' thing to see if the engine dies?

Then back them back out to make adjustments?

Secondly,
Main Jets have ABSOLUTELY NOTHING TO DO WITH IDLE FUEL.
All idle fuel is metered through the idle mixture screws.

Your Main Jets won't take over until about 1,000 or 1,200 RPM,
AND,
There will be a transition over from idle mixture screws to main jets starting somewhere between 800 RPM and lasting to about 1,200 RPM.

The Accelerator Pump and Power Valve are there to help smooth that transition out as you switch from Idle circuits to Main Jet circuits in the carb.

Idle SHOULD be a little lean...
To fatten up the Idle mixture means you are wasting fuel!

(although I have to admit, I usually find the best vacuum,
then 'Fatten' up the fuel a little, just about 1/8 idle mixture screw turn on both screws, since I sometimes idle with my engine pulling in gear)

Quote:
It was getting late at that time so I pulled the plug wires and distributer, just so I could have it ready for inspection when I got to that point.

Thinking more about the issue, and reading these posts, I am beginning to believe that it may have been jets because the ported vac line going to the dist that I disconnected to check centrifugal was not plugged.

Makes sense, air coming in from a point that does not have a say on the amount of fuel that gets metered with it. "Alien Air".
What you call 'Alien Air', we call a VACUUM LEAK!

Quote:
So that issue may be just a cause of operator error on my part, or maybe I'll blame the wife. hehehe.
If you can't blame your wife, blame my 'Other Half'

-----------------------------------------------------

Quote:
Either way, I'll have to re-check that after I figure out the dist issue. Haven't yet checked spark or voltage at the coil/module.
What rich isn't getting a grip on...
There is a BIG DIFFERENCE between "Will Work",
And 'OPTIMUM PERFORMANCE' for any given set up...

Your coil WILL fire reliably with about 4 or 4.5 volts (E-core)...
It's only going to produce about 15K or 18K volts for the plugs (same as breaker points ignition with resisted coil),
But the spark will be RELIABLE up to about 2,000 RPM on a V-8 engine.

*IF*...
You want MAXIMUM OUTPUT from your Upgrades,
You need to FEED the ignition coil!
We are talking AT LEAST a 12 gauge, unresisted wire,
And preferably a 12 gauge that doesn't have two dozen wiring connections to go through getting to the ignition coil...
(Starter Relay Fusible Link to primary fuse block wire,
Fuse block, connectors to ignition switch,
Connectors FROM ignition switch, factory tach (if you have one),
Then bulk head connector, harness connectors,.....
You get the idea, one corroded, old, dirty connector, and suddenly the coil is starved for sufficient supply for MAXIMUM output...)

Anyway,
Taking the factory resistor wire out will gain you quite a bit of current to the coil,
Using a power relay instead of beating the power to the coil through the fuse block and ignition switch will gain you some,
Making sure you use the correct wire size will gain you some...

You get the idea! (even if some people don't!)

Quote:
TR: That picture shows the weights and (basically)limiters, correct?
YES.
The Weights are clearly visible,
The return springs are what controls the movement of the weights as centrifugal force tries to pull them outward.

The slots are the limiting of the advance/retard of the centrifugal advance head that fits on the actual distributor shaft....

This is a centrifugal advance head off the distributor shaft.




CLEANED Distributor Shaft! (harder than it sounds!)





Centrifugal Advance Head Mounted On The Shaft,




Quote:
Replacing springs and weights is a means of adjusting how fast/slow, sooner/later the ignition advances, given different variances.
Correct.
It's the TOTAL spring rate,
NOT MATCHED SPRINGS that will get you the advance 'Curve' (on a graph) you are looking for.

Two heavy springs, one heavy and one medium, one heavy and one light, two mediums, one medium and one light, two light springs....
IT's the TOTAL SPRING PRESSURE...

I say again,
THE SPRINGS DO NOT HAVE TO BE 'MATCHED' PAIRS!



Quote:
If a person were to replace the springs and weights, in a non high performance application, like mine, they would stick with stock weights and springs, right?
Springs I change without ever thinking about it...
And I haven't found any reason to change the weights on a Jeep distributor.

See, your distributor is optimized for EMISSIONS!

Not necessary for the best power for your vehicle!

I don't think twice about adjusting the centrifugal advance, no more than I do sticking an 'Allen' wrench in the vacuum advance and adjusting that for more power or smoother performance.
---------------------------------

Quote:
If so, where would that person find these stock weights and springs, short of a bone yard?

Not Napa, Autozone, or Oreillys, the local jeep dealer doesn't have them, nor can they order them.
Mr. Gasket, p/n 925D,
Also, any of the 'Discount' parts places,
Just ask for a spring kit for a GM HEI distributor, the springs are the same for both the Jeep/Motorcraft and GM HEI distributors with centrifugal advance.

Quote:
The local ford dealer is in the same boat.
They all require the purchase of a new or rebuilt distributor.
But, I haven't inspected mine yet so I'm not sure if its broke as of now.
Dealers aren't going to have centrifugal or vacuum advance parts.
The last 10+ years of distributors haven't had either advance in them,
And most of the better engines don't have distributors anymore!

Quote:
I'm gonna stick with my 7.5 PV for now.
PTC is at 10hg. 2 down is 8, so my options are 7.5 or 8.5.
I'll probably check out an 8.5 eventually, after I correct the distributor.
For a PTC of 10 In.Hg., about 7.5 is correct for off road/highway driven.
It will load the engine up on fuel when you are trying to 'Finesse' an obstacle at low RPMs, but still give you reasonable street performance.

Quote:
BTW, I am currently running the TFI with HEI module set up. It's all wired up as per the directions given, with correct gauge wire and relay.
Then you DO NOT have a resistor in line if you are using a power relay for the coil power...

Then with a 0.040" or 0.045" plug gap and reasonable plug wires,
You are probably throwing 35K to 40K at the plugs under 2,000 RPM.
With the Ford E-core coil, you are probably getting slightly better saturations times (shorter time to full saturation),
So you are probably looking at around 2,200 or 2,300 RPM before the AMPERAGE and DURATION times start to drop off significantly.

So Many Cats, So Few Recipes...

Last edited by TeamRush; 07-04-2009 at 01:53 AM.
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post #26 of (permalink) Old 07-04-2009, 01:55 AM
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Quote:
(*EDITED FOR BREVITY*...)
Will a "weak" spark not be enough to combust the mix?

I'm thinking, as long as the spark is enough to create combustion with fuel, the intensity does not make a difference.
HUGE DIFFERENCE between Hot, Solid Ignition,
And a fast, weak spark that might not be hot enough to get the mixture burning throughly...

Poor ignition leads to SLOW BURN TIMES.
Slow burn times leads to raw fuel being blown out the exhasut valve,
Reduced power rates,
Increased emissions,
Plugged converters and mufflers,
Overheated exhaust components and exhaust valves...
And a TON of acids being formed in the exhaust.

You are looking for a HOT, SOLID IGNITION so you get a proper flame front moving across the combustion chamber,
Getting into every edge, under every overhang, in around valves, ect.

If you don't have that, well, you are wasting gasoline and making pollution.

There is a REASON MSD modules are CARB certified,
Because they clean up emissions simply by getting the fire lit!

I don't know ANYONE that has done the large cap/tall rotor, plug wire upgrade that didn't pick up 3 or 4 miles to the gallon and have smoother running, easier starting engine...

Simply because the fire is actually getting lit in the cylinder!

When you throw a CDI module at the system,
You INSTANTLY INCREASE USABLE SPARK ENERGY BY 500% to 1,000%!
The spark is FULL STRENGTH at each firing, and the plug simply fires 5 or 6 times per firing cycle,
Where your factory ignition fires ONCE (if you are lucky!),
And the factory ignition starts to loose spark energy VERY QUICKLY,
Usually around 2,000 RPM on a V-8 engine,
So by the time you reach 5,000 RPM,
You are back down to breaker points voltages,
And the Amperage & Duration are virtually missing!

CDI goes to single fire on a V-8 about 2,500 RPM (no time to fire each plug 5 or 6 times with the crank moving that fast)
But the CDI keeps that same 35,000 or 40,000 Volts and full Amperage/Duration discharge all the way up...
Much higher than you can rev an AMC ENGINE!


Quote:
Anyway, a spark occurs within an instance, whether weak or strong. doesn't the fuel ignite either way?
Nope, not even close!
You wouldn't believe how much unburned hydrocarbons flow right out the exhaust pipe or wind up in your oil!

Quote:
And once that fuel is ignited, it completely combusts because of itself combusting, not because a spark was so intense that it scared it into complete combustion.
Nope, depends on the flame front in the combustion chamber.
If the spark is weak and thready, you will get 'Fire' lingering around in one part of the chamber and not moving across the chamber like it's supposed to...

Even the way the ground electrode faces in the chamber can cause problems with the flame front....

And you have to remember, this isn't just a high pressure fuel/air (Charge) mixture setting static in the chamber,
With 'Quinch' areas, gasket protrusion or cavity between cylinder and head,
Carbon deposits, intrusion by valve rims, domes on pistons, thermal currents, ect.

That fuel mixture is SWIRLING around in the chamber something like a tornado on steroids...
So if a short duration, weak spark encounters a 'Lean' spot in chamber,
Or worse yet, a pocket of left over exhaust gas that didn't get scavenged out,
Then that spark might just fizzle and not do anything...

But a good HOT spark would get even the lean mixture pocket lit...
And a LONG DURATION spark would be in the gap long enough to 'See' much more of the charge mixture as it swirls around in the chamber, and get some of the richer parts of the mixture started burning properly.

With a CDI module, you get 5 or 6 FULL STRENGTH, FULL AMPERAGE and FULL DURATION changes to get that fire lit properly,
And after about 2,500 RPM, when you don't have time for 5 or 6 full on chances to get it lit, you get a SUPER SINGLE SPARK DISCHARGE to get the charge lit...
(Remember, with ANY factory single fire module, you are WAY DOWN on spark energy, voltage, amperage and duration by the time the CDI module is still giving you one FULL STRENGTH/DURATION spark...)

Quote:
That is what's going through my mind as I search out reasoning as to why I'm looking for a blue spark snapping and popping like a platoon of Marines in Boot Camp performing rifle manual during final drill, which, BTW, is an amazing sight for those of you who haven't experienced it.
Parris Island, class of '78,...
ain't no hollywood marine!

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post #27 of (permalink) Old 07-04-2009, 02:01 AM
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Quote:
Originally Posted by Caver Dave View Post
Ethiopia?

And so as not to completely derail your thread & to corroborate Rich's statement on the potency... I've previously ran points & TR/TFI ignitions and was "bitten" by both, not *that* bad. All I know is after recently swapping in the TBI system (which requires my old MC dizzy to signal the 7pin "HEI" [EST] module & GM TFI coil), it will light you slam up! The effect IMHO is minutely less than being tazored... same intense pain, same loss of involuntary bodily functions, same "coming to" moments later wonder WTF just happened,... just no LEO shouting to stay down
How bad you get 'Zapped' is directly proportional to how well you are grounded!

Leaning over the fender on sweaty arms or hands,
or having a sweaty hand on an engine bracket when you get 'Nailed' will give you a GREAT ground,

And if you go hand to hand (most people don't),
you move the current across the heart!
Remember this CAN KILL YOU if you are grounded solid enough and the strike hits you at the right place in the natural cycling of your heart!

Wait until you get a hold of an MSD 8 or 10 box that throw enough amperage to actually kill you outright!
I've seen an MSD 8 box (and correct coil) throw a foot long spark to a shelving unit while it was on the distributor machine!

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post #28 of (permalink) Old 07-04-2009, 09:58 PM Thread Starter
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Quote:
Originally Posted by TeamRush View Post
I don't know ANYONE that has done the large cap/tall rotor, plug wire upgrade that didn't pick up 3 or 4 miles to the gallon and have smoother running, easier starting engine....
Mileage stayed the same for me, 10ish.

Quote:
Originally Posted by TeamRush View Post
Something WRONG there,
You should have had about AT LEAST 5 to 7 come in, even with the later computer versions of the distributor....
It would actually seem to initially retard a degree or two before holding steady at 10 from idle up to 2k. That timing chain does not hold up for very long. I believe that's the culprit of the initial retardation.



Quote:
Originally Posted by TeamRush View Post
I can't imagine what is keeping the centrifugal advance from working...
Normally the centrifugal advance is bullet proof in the Ford type distributors!
GM HEI Distributors used to waste the advance weights in fairly short order, but Ford distributors chug along for ever without problems...
There were two springs in my dist. one heavy, and the other I would consider medium. I removed the heavy and in its place I put the medium. I then installed a lighter one where the medium originally was. I found a set from a long time ago that I had saved. Put it all back together and back into the jeep. The ignition advanced to about 16 with no vac. But the mark on the dampner would disappear and reappear randomly. Probably caused by the plug clamp being too close to the #2 wire or it not firing...it was a quick check, didnt have time to mess around with it a lot.



Quote:
Originally Posted by TeamRush View Post
First off,
Did you do the screw the idle mixture screws 'IN' thing to see if the engine dies?

Then back them back out to make adjustments?

Secondly,
Main Jets have ABSOLUTELY NOTHING TO DO WITH IDLE FUEL.
All idle fuel is metered through the idle mixture screws.

Your Main Jets won't take over until about 1,000 or 1,200 RPM,
AND,
There will be a transition over from idle mixture screws to main jets starting somewhere between 800 RPM and lasting to about 1,200 RPM.
I did not turn them in to see if it died. I started at 2 turns out each and adjusted evenly from there.
Since the main jets don't come in until around 1k, I was thinking they may be a little small for my application given the issue I said earlier. Or, it could be having a problem with the transition because it would only stumble with a slow increase of rpm, not with a throttle blip.

Quote:
Originally Posted by TeamRush View Post
The Weights are clearly visible,
The return springs are what controls the movement of the weights as centrifugal force tries to pull them outward.


It's the TOTAL spring rate,
NOT MATCHED SPRINGS that will get you the advance 'Curve' (on a graph) you are looking for.

Two heavy springs, one heavy and one medium, one heavy and one light, two mediums, one medium and one light, two light springs....
IT's the TOTAL SPRING PRESSURE...

I say again,
THE SPRINGS DO NOT HAVE TO BE 'MATCHED' PAIRS!
should the heavier spring be on the weight marked 13R or is it the other way? does it matter?

'88 YJ
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post #29 of (permalink) Old 07-10-2009, 07:03 AM Thread Starter
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After some thinking, I've came up with two theories:
1. Original problem was caused by my centrifigual advance not operating properly, not advancing. Now, with a lighter spring in place of the heavy one in the dist., the ignition advances but slightly retards prior. The issue there might be too light of a spring causing the advance head to not respond as quickly as the dist. shaft i.e., the shaft turns but the head takes a second or two to catch up.
2. Original problem caused by a distorted valve in the accelerator pump housing, against the carb making the shot of fuel visible but weak and with little volume. this is corrected by replacing the valve and accel pump while I'm at it. That's done, problem exists still. The issue here might be some pitting or slight scores in the carb body that need to be cleaned up in order for the valve to seat properly so a stronger shot with more volume of fuel can be obtained.

What are your thoughts?

'88 YJ
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post #30 of (permalink) Old 07-10-2009, 09:56 AM
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Quote:
Originally Posted by USMCYJ View Post
2. Original problem caused by a distorted valve in the accelerator pump housing, against the carb making the shot of fuel visible but weak and with little volume. this is corrected by replacing the valve and accel pump while I'm at it. That's done, problem exists still. The issue here might be some pitting or slight scores in the carb body that need to be cleaned up in order for the valve to seat properly so a stronger shot with more volume of fuel can be obtained.

What are your thoughts?
Can you move the accel pump linkage further away from the throttle shaft center? This should actuate the accel pump a little more equaling more volume, right?

Caver Dave
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