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post #1 of (permalink) Old 04-11-2002, 11:52 AM Thread Starter
 
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Vacuum advance options for Duraspark

I read in some older posts (thank you for the return of Search [img]images/icons/smile.gif[/img] ) that the stock computer used solenoids to control a varying mix of manifold and ported vacuum to send to the distributor for a vacuum advance signal. My emissions stuff is long gone, I have a 4.0 head on the 258 now (so the combustion chamber is completely different), and my intake (Clifford 47-4500-WH) doesn't have places for the stuff anyway.

I'm pretty sure that the stock mechanical advance springs are what I need in the Duraspark. I have heard about aftermarket ones that are lighter and allow the mechanical advance to come on quicker, but right now I need slightly less total advance in the 1500-2000 range.

What options do I have (if any) for a vacuum advance mechanism on the Duraspark distributor. Anything off another distributor that I could try cheap? Anything available aftermarket with an adjustable advance? Any ideas on rigging some kind of modifier or control?

What about trying some lighter mechanical springs in combination with running manifold vacuum instead of ported (right now I am running straight ported)?
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post #2 of (permalink) Old 04-12-2002, 11:49 AM
 
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Re: Vacuum advance options for Duraspark

*87 YJ hardtop 258 w/4.0 head, Crane 260, Clifford intake, Holley 390, Borla header.*
You should put this at the top of your post so I don't have to go chase it down...
<hr>
You haven't described under what circumstances you are having this 'Problem' or even what the 'Problem' is...
We don't know if the vehicle is spark knocking, missing, bogging (falling on it's face when trying to accelerate), cutting out before taking off when you depress the throttle, or what's going on.
You just said you have a 'Problem' between 1.5K &amp; 2K....
<hr>
Just between me and you, I'd think that it's a fuel problem at just off idle way before I'd think a stock distributor is the problem...
At the RPM you quoted as the problem, (1,500 to 2,000 RPM), I'd come more of thinking that you are having a transition problem between the high idle circuit and the main fuel circuit in your new Holley... (especially with headers...)
But that's just me...
<hr>
What have you done to your distributor/ ignition so far?

If you haven't already upgraded the ignition to the 'TeamRush' ignition upgrade, you may be experiencing cross fire in the cap.

Starting with the larger cap and rotor, better plug wires, and a coil that is controllable is a good start.
<hr>

You need to move your vacuum advance source from baseplate or manifold vacuum to a 'Spark Ported' vacuum source.
(The call it 'Spark Ported' for a reason...)
-----------------

You need to check to see if you have the type of vacuum advance that has a limiting screw built in to the diaphragm assembly.
You may be able to limit total vacuum advance like that.
(Look in the nipple where the vacuum hose connects, there will be a screw through the vacuum diaphragm that limits travel of the diaphragm.)
Your adjustment may already be built in...
----------------

More than likely, you need one heavy (Jeep factory heavy, not tune up kit heavy) and one medium spring.
Jeep used a heavier spring than Ford did for passenger vehicles.
(The only time I've seen a spring that heavy on a Ford vehicle was on farm trucks.)

If your distributor has been apart, and the 'mechanic' didn't know exactly what he was doing, you may be getting way too much mechanical advance.
The advance head has two limiting slots in it, (See Graphic).
One is moderate, while the other is the built in 'Lets Go Racing' advance slot.


You will find a plastic 'Bump Stop' around the advance slot limiter arm.
(If you find you don't have one, at least use a nylon wire tie to replace the bump stop)
Using a piece of thick rubber tubing (like vacuum line) over the limiter arm will decrease the total centrifugal timing by just 3 to 5 degrees.
-----------------

You can also (and I'm not recommending this) drill holes in the advance weights.
Lighter weights take more RPM to extend them with the same spring pressure.
This is a last resort when you can't time the advance any other way.
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post #3 of (permalink) Old 04-12-2002, 03:53 PM Thread Starter
 
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Re: Vacuum advance options for Duraspark

I apologize for leaving holes in my information. Let me address that first:

Wieght and Gearing
87 YJ Hardtop: tools in back but otherwise no heavy accessories
Puegot BA 10/5
NP 231
Dana 35C (3.07 gears)
worn 31" Mud Kings (turns roughly 2100 @ 80mph in 5th and 2700 in 4rth if I remember right)

Engine
258 block: ~3K on a .040 over rebuild, stock internals except for Crane 260H cam. Donor was a 79 CJ that I never saw.
4.0 head: new, stock 95 Model. Casting #7120. (From a company called Alabama? - not sure.)

Induction
Clifford 47-4500-WH intake: from donor engine.
Holley 390: new, Model 4160 (vac sec for those unfamiliar with Holley), P/N R8007, primary jets changed to 57's today (see below).

Exhaust
Borla header for 95 4.0
2 1/8" pipe with muffler only (not sure what kind of muffler).

Ignition
Stock 87 model distributor base (have yet to inspect internals). Vacuum advance is hooked straight to Ported Vacuum on the Holley.
Spacer with Conrad all-brass cap (from TR upgrade).
Taylor 8mm spiral wound wires.
Champion truck plugs gapped to .045
Accel SuperStack coil (inherited from donor block)
MSD 6A
Timing set to 8* BTDC @ 1600 rpm w/vac advance isolated.

Driving habits
95 percent street (daily driver).
I rarely see the high side of 3K and almost never over 4K. Primarily drive between 1500-2500.
93 octane gas.

Description of original "Problem"
Spark knock @ moderate throttle openings between 1500-2000 rpm at highway speeds. I only hear it when in 4rth or 5th gear, flat or inclined road. I realize that smaller amounts of detonation can happen without hearing it, but I haven't hooked up a mechanical stethoscope yet. Seems to be worst around 1600.

I would like to be able to run either more advance (for better go-pedal response, especially down low) or lower octane gas. Either one would make me happy. Better gas mileage would be nice too (right now my best is about 15mpg from a day of driving conservatively on 50mph roads), but right now I'll take what I can get.

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

From my first read of Dave Emanuel's Super Tuning book and my limited past experience (the old addage: a little knowledge is a dangerous thing), I was initially under the impression that timing problems needed to be solved before addressing the carburetor. In the process of getting feedback from other posts, re-reading Dave's book, and talking to a mechanic friend, I am realizing that both can cause detonation and getting the impression that things tend to be more of a back-and-forth kind of feedback loop (no reference to the BBD intended).

I put the MSD 6A on Monday night and it made a significant difference, both in power and in cutting out a fair amount of the detonation. Yesterday I finally had the chance to pick up some new jets, a set of 54's and 57's.

This morning, before changing jets, the spark plug insulators were white with a small patch of semi-glossy black that looked almost crackly, like it might be starting to blister. No visible exhaust emissions.

Changed stock 51's out for the 54's. No visible change in insulator appearance. Still no visible exhaust emissions.

Changed 54's out for the 57's. Started to get a little bit of grayish-tan on the lower half of the insulator. Have not heard the spark knock yet. Still no visible exhaust emissions. Maybe I can tell that it is running a little better, maybe it is just me wanting to feel it and an overactive imagination.

This morning I also hooked up a hand held vacuum gauge to manifold vacuum and ran it under the frame and in the driver's triangle window. Trying to drive while holding it was an interesting experience, but I found the following:

Idle: 16" steady
Steady 50mph on flat road, 4rth gear: 14"
Interstate is hard to judge flat, steady state. (I live in upper east Tennessee. Very little is flat for long.) I mostly saw around and maybe a little above 10".
I was very surprised at how easily it dropped. Light acceleration and it was around 10". Not much more throttle dropped it to below 5". Combine a hill with moderate throttle and vacuum went away completely.
Deceleration from upper revs I saw as high as 26", 27" maybe.

I'm wondering if a two-stage power valve would benefit me and if so, which one. I also have a secondary spring pack that I was going to tinker with, but taking off the choke to then take off the secondary diaphragm housing seems like kind of a hassle if you're going to try several. Am I understanding that right?

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

In response to a few things you mentioned, TR...
-If I had "a transition problem between the high idle circuit and the main fuel circuit", how would I address it?
-I posted something a while back about the Accel coil vs. a Blaster 2 or TFI and you told me not to "grind my brain" on it. Should I re-consider this?

I will pull apart my distributor hopefully sometime this weekend to inspect the springs, limiter, and look in the nipple of the vacuum advance diaphragm housing. Will most parts stores carry the springs I need if I don't find the correct ones in there? What make/model should I ask for?

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

Thanks for all the help. I'm getting there and learning a bunch in the process (or at least would like to think so).

|-D
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post #4 of (permalink) Old 04-12-2002, 06:34 PM
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Re: Vacuum advance options for Duraspark

I getting ready to tackle a similar issue this weekend, and it occurs to me that I have never really seen a really good reference for reading plugs. I have the old color center section in the chiltons, but I have never had a plug resemble any of their photos. TR, any suggestions? Brendan
post #5 of (permalink) Old 04-12-2002, 06:42 PM
 
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Re: Vacuum advance options for Duraspark

What do you mean PROBLEM!?
If you are running 80 MPH in 5th gear, you don't have any problems!!![img]images/icons/blush.gif[/img]


That's like the old woman with a Virginia ham under both arms and complaining because she doesn't have any bread!!!!

Some of these guys cant get up to 50 MPH with out the engine jumping out on the pavement!.....
<hr>
*Spark knock @ moderate throttle openings between 1500-2000 rpm at highway speeds. I only hear it when in 4rth or 5th gear, flat or inclined road.*

You have too much for the load/ fuel/ total advance at that RPM.
We'll get back to this in a minute...
----------------

*This morning, before changing jets, the spark plug insulators were white with a small patch of semi-glossy black that looked almost crackly, like it might be starting to blister.*

Those are detonation bubbles starting to form.
You have a SEVERE detonation problem, and if you don't do something in short order, you are going to hammer the engine to death.
-----------------

*Changed 54's out for the 57's. Started to get a little bit of grayish-tan on the lower half of the insulator. Have not heard the spark knock yet. Still no visible exhaust emissions. Maybe I can tell that it is running a little better, maybe it is just me wanting to feel it and an overactive imagination. *

It probably is running a little better, you are not dead lean all the time now.
You are shooting for a very light caramel brown/tan color on the porcelain of the plug, that will be closest (safe) way to judge your fuel mixture with out a rich/lean indicator.

I think you are on the right road here...
Dave Emanuel's Holley tuning book is the best 'Quick Text' I've ever seen on tuning Holleys.
------------------

*Idle: 16" steady Steady 50mph on flat road, 4rth gear: 14"
Interstate is hard to judge flat, steady state. (I live in upper east Tennessee. Very little
is flat for long.) I mostly saw around and maybe a little above 10".
I was very surprised at how easily it dropped. Light acceleration and it was around 10".
Not much more throttle dropped it to below 5".*

Looks like you need a power valve that opens at 5 or 5-1/2.
Give me the list number off the front of the choke horn of your carb, and I'll tell you what your power valve is *SUPPOSED* to be... (we all know that unless you buy one new, Holley power valves are NEVER stock...)
------------------

*In response to a few things you mentioned, TR...
-If I had "a transition problem between the high idle circuit and the main fuel circuit", how would I address it? *

By fattening up the idle to meet the main circuit that gets drawn through the jets, or by changing jet sizes to meet the idle mixture...

In extreme cases (And I'm NOT selling this as a home game, you can screw up the carb QUICK! and forever!) you can undersize/ oversize or taper inlets to the emulsion vent tubes to micro adjust the mixtures, but remember, those changes are permanent!
------------------

*-I posted something a while back about the Accel coil vs. a Blaster 2 or TFI and you told me not to "grind my brain" on it. Should I re-consider this?*

Nope, that MSD 6 module will make ANY coil a fire breathing dragon!
The Accel Super Stock isn't anything but a premium quality (Factory Grade) stock canister type coil anyway...
Don't be fooled by the yellow paint and sticker...
It's just a factory Ford coil wearing a yellow dress.[img]images/icons/tongue.gif[/img]
-------------------

*I will pull apart my distributor hopefully sometime this weekend to inspect the springs, limiter, and look in the nipple of the vacuum advance diaphragm housing. Will most parts stores carry the springs I need if I don't find the correct ones in there? What make/model should I ask for? *

1. All you have to do is take the reluctor off, and take the floor plate out of the distributor to inspect the lower end. If you take the advance head off the shaft, be very careful of the little circle clip, it's easily lost/ broken and virtually impossible to replace.

Make sure you mark the slot on the reluctor your distributor was using (There are two, one is retarded)
Don't loose the tiny roll pin that holds the reluctor in place,
Don't destroy the wire 'C' clip that holds the mag trigger plate in place. This is not a commonly available item.

2. You will not be able to find that heavy factory spring in the parts stores, and I haven't even seen one on the Jeep reman distributors, they all have two mediums when I get them.
If you need a heavy one for some reason, let me know, and I'll pop for the $0.34 for the stamp and send you one...

3. Inspect for the advance slots.
One should be around 13, and one around 18. (a few differences in year models, but that is how most are)
Use the 13 degree slot, and make sure there is a plastic 'bump stop' clip on the advance slot limiter.
If you want to knock back the total centrifugal advance a little, use a piece of heavy walled rubber tubing or a heavy (and wide) wire tie around the plastic clip that is already there.
This will take another 3 to 5 degrees out of the centrifugal advance.

4. If you don't see something like...
A. broken, missing, or undersize springs,
B. Advance head stuck in full advance, or weights that won't retract or don't have plastic bushings,
C. Limiter arm bent, missing, or missing the plastic 'bump stop',
D. Limiter arm in the '18R' advance slot instead of the '13R' advance slot,
Then put the damn thing back together and stop screwing with it!

While you have the advance plate out, why not replace the "Mag Trigger Pick Up Plate" with a new mag trigger?
It's about $10 to $15 and will make one more thing you don't have to worry about.

A new vacuum advance should still be available for that distributor, since Ford was still using it until 1990.

Here is a Money tip, price the vacuum advance, the mag trigger, ect, and see if a reman distributor is much more expensive.
Most of the time you can get a reman distributor for about $20 more.

Strip the core of all good parts, Like springs and gear, before you return it.
----------------

What I'd start with is to richen up the idle mixture about 1/4 turn each on the idle mixture screws,
(And test for the detonation)

I'd go up at least 3 jet sizes, (you have already started in that direction)
(And test for the detonation)

I'd test for ruptured diaphragm and adjustable diaphragm in the vacuum advance.
You may be able to limit some of the advance there...

I'd knock my timing back 4 degrees at a time (and test for detonation) until the detonation was gone.

Remember, when you have eliminated the detonation (unless you find something broken or real wrong) you will have to drop at least another 3 or 4 degrees of total timing after all noticeable symptoms are gone.
There will still be detonation you can't detect with feeling or ears, and you really need to kill that too.

'Knock' detectors (detonation detectors) are a great idea.
<hr>
Let me say something about your ability to get the information out...

After I stuck you with a fork, you did a great job of filling in the blanks!
The Vacuum readings was above the top! That's exactly what I needed to decide on a power valve!
I wish everyone would research the problems the way you did before asking for advice. If they did, they could ask coherent questions and get proper answers back...

Good job and keep me posted on the progress.
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post #6 of (permalink) Old 04-12-2002, 06:51 PM
brendan
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Re: Vacuum advance options for Duraspark

'Knock' detectors (detonation detectors) are a great idea.


could you elaborate on exactly what these devices are? obviously they detect knock with a microphone, but do they sned this data to a guage or light or what? Thanks, Brendan
post #7 of (permalink) Old 04-12-2002, 07:12 PM
 
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Re: Vacuum advance options for Duraspark

You hit the head right on the nail...
In most cases, you get a dash board indicator with LED lights that tell you when detonation is present.

With MSD ignitions, you can install a detonation sensor on the block, and with the help of an add on module, the ignition will retard the timing automatically until the detonation is gone.
The secret here is to jack the timing up so you get full Horse power, then let the knock detector set the timing back until the knock is gone, that way you are always at maximum power with out knock...
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post #8 of (permalink) Old 04-12-2002, 07:28 PM Thread Starter
 
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Re: Vacuum advance options for Duraspark

Okay, so call me power hungry. I won't blush [img]images/icons/cool.gif[/img]. I wanted to put a 350 in this thing and couldn't afford to do the transmission swap at the same time.

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

Looks like you need a power valve that opens at 5 or 5-1/2.
Give me the list number off the front of the choke horn of your carb, and I'll tell you what your power valve is *SUPPOSED* to be... (we all know that unless you buy one new, Holley power valves are NEVER stock...)


It is a brand new Holley P/N R8007. So unless they hosed it up from the factory, I should have a 125-65 for a power valve.

What would you think of using a two-stage power valve, like maybe the 125-207 or -208?

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

I will take the steps you mentioned on idle mixture, jet size, vacuum diaphragm testing, and total advance settings.

Would it be appropriate for me to change the original subject of this thread to something like:

"Detonation problems: Holley/ignition system tuning"

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post #9 of (permalink) Old 04-12-2002, 07:44 PM Thread Starter
 
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Re: Vacuum advance options for Duraspark

Okay, searching MSD's site I found their "Engine Knock Alert" module (P/N 8964) and they make reference to using it in conjunction with their "Adjustable Timing Control" module, but that is a manual device. Is there another module or plug-in that can plug into the 6A and automatically retard the timing?
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post #10 of (permalink) Old 04-14-2002, 10:19 AM
brendan
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Re: Vacuum advance options for Duraspark

TR, you wrote:

"What I'd start with is to richen up the idle mixture about 1/4 turn each on the idle mixture screws,
(And test for the detonation)

I'd go up at least 3 jet sizes, (you have already started in that direction)
(And test for the detonation)

I'd test for ruptured diaphragm and adjustable diaphragm in the vacuum advance.
You may be able to limit some of the advance there...

I'd knock my timing back 4 degrees at a time (and test for detonation) until the detonation was gone. "

(test for detonation)? Are you talking ears or reading plugs?


Thanks, brendan
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