Need Dual Point Assistance

[Dragon Slayer]

You need to validate the cam stop on this distributor. Since this is not original to the car, you may have a mix of parts installed. The cam stop has a 2 letter designation underneath. This is the last 2 of the part number and I can validate what distributor it comes from via the Autolite/Prestolite parts manual. Second you need to inspect and measure the slots for wear and help in determining how much mech adv that cam stop adds. Then measure pt to pt on the cam, I can tell you if that is stock measurement, worn, or a cam stop from a single pt distributor (they are similar for early ones). On the vacuum adv arm, there is a number, like 8, 9.5, 12 that is the max vacuum advance applied. Spring and shims provide the curve. How did you test? You can remove nipple and spring/shims and blow on it, does it hold pressure? If not diaphragm is gone and you will just have a vacuum leak with hose attached.

If you have a volt meter you can attach to distributor lead and body and watch and measure resistance as you slowly rotate distributor shaft. You want near zero resistance when either point closed. One may not be giving you that.

A true early Prestolite can handle the 8 to 12 initial timing because mechanical was only about 20 total. Later cars were CAP or CAS cars and initial timing was 0 because distrib provided 30-32 degrees mechanical advance (at crank).

Hard to see in second picture, but if you look at about 3 o'clock you can see LU stamp. That is the later 440/hemi cam stop with 15 degree mechanical which gives 30 total. Cars that need initial set at 0 degrees.

 

[HALIFAXHOPS]

Dragon. Any chance I can get a copy of the pages? Just been writing them down been looking for a autolite parts book for years.

 

[Dragon Slayer]

Dragon. Any chance I can get a copy of the pages? Just been writing them down been looking for a autolite parts book for years.

Autolite has 1-3 pages by distributor number. So not like I can just copy the data you need. Can answer a specific question for a specific distributor though. Worth getting one though.

 

[HALIFAXHOPS]

I need to either get a copy or buy one! You game for a copy?

 

[lyndondb]

get rid of the points and replace with electronic. Module fits right in your distrubutor.
Replaced mine over 20 years ago with no problems.

 

[HALIFAXHOPS]

Autolite has 1-3 pages by distributor number. So not like I can just copy the data you need. Can answer a specific question for a specific distributor though. Worth getting one though.

Where can I find one? I have picked up a few autolite parts books and they are very lacking. Prestolite is even worse unless I spend 200 on a full shop parts manual for a few pages.

 

[Dragon Slayer]

I got mine off the bay. The AL was several hundred pages and covered the 40 to mid 60s including the superstock distributor. Pretty funny with the FORD logo on the pages of a distributor for a MOPAR race car. Prestolite did start to consolidate, but I got a manual that covered the gap for MOPAR. Then I picked up an AL Service manual. Unfortunately that only went to the early 60s. I did this because you really can only get vague information on net. No one ever answered the letter stamping questions I asked about cam stops, or the various clocking and part numbers on shafts. So I figured it all out myself. Each distributor type had unique parts when it came to shaft, cam, and vacuum cannister.

The ability to cross reference common parts has been really great though. But much of this still has to be done by site of a known part, because only the Shaft and the Cam Stop and some condensers have part numbers on them. MOPAR did put their part number on some vacuum cannister, but AL did not. Breaker plates, point, and housing do not, though they do have assigned part numbers in the books. You also have to cross reference to Service Manuals to isolate what the mechanical and vacuum advance rates are. That help put the slot length measurement to a max degree and also clarify what vacuum bodies go to what distributors. There might only be 5 vacuum body types (max advance stamped on arm) covering 15 similar distributor numbers and the only difference is a spring type and number of washers. So I can even build a correct vacuum advance.

I just do this for my own enjoyment, so I invested in the manuals. I do document all the variances in the distributors I have bought though. Primarily Big Block Dual point types.

I have picked up undesirable NOS distributors just to harvest NOS parts to build a complete distributor. I build this one with all NOS parts except the housing and shaft which I picked at Carlisle as an incomplete distributor. Back up for my Hemi car.

 

[67 GTX]

I do not have any record on what my cam stop says underneath, just what it has on top, which is a "E"
I follow your statement on different distributors require different initials based on what their curve is. Funny thing, the FSM doesn't even show a dual point for a 440 in 67.

So I set out tonight to try and figure out some characteristics on my distributor.
I set the initial timing to 0, and rev'd the motor. I got a bit more than the last timing mark on the timing cover, so lets call that 13 degrees of mechanical advance.

I am running a 4326s carb, so I only have the option for carb. vacuum.

With initial timing still at 0, I hooked up the vacuum advance. No change in timing.
Tried to rev the motor, would instantly stumble. Unplugged vacuum advance, rev'd fine.

Pushed initial timing to 12 advanced, no vacuum, revs fine. Hook up vacuum, stumbles. Won't actually rev at all from idle.

Pushed initial timing to 20-ish, with vacuum, and same result, complete stumble. Keep in mind, this is all done while in neutral.

Dwell is at 38 degrees. Max carb. vacuum was 23 in.

Not sure how the vacuum is causing an issue here. I think I debunked the theory of it over-advancing, since I tested for that by giving the car 0 initial timing. That gave it a lot room to advance if it wanted too.

Keep in mind, with my older distributor, I always ran 12 initial (before hooking up the vacuum advance), as well as the vacuum advance, and the car ran great.

 

[miller]

Funny thing, the FSM doesn't even show a dual point for a 440 in 67.

I have a copy of the 67 FSM, and looked. Yes, Prestolite dual point is in there, under ignition, V8. 440, if it's covered in 67, wouldn't matter, RB motors the same.

Tried to rev the motor, would instantly stumble. Unplugged vacuum advance, rev'd fine.

Really sounds like somethings amiss with your vacuum advance.

 

[HALIFAXHOPS]

I got mine off the bay. The AL was several hundred pages and covered the 40 to mid 60s including the superstock distributor. Pretty funny with the FORD logo on the pages of a distributor for a MOPAR race car. Prestolite did start to consolidate, but I got a manual that covered the gap for MOPAR. Then I picked up an AL Service manual. Unfortunately that only went to the early 60s. I did this because you really can only get vague information on net. No one ever answered the letter stamping questions I asked about cam stops, or the various clocking and part numbers on shafts. So I figured it all out myself. Each distributor type had unique parts when it came to shaft, cam, and vacuum cannister.

The ability to cross reference common parts has been really great though. But much of this still has to be done by site of a known part, because only the Shaft and the Cam Stop and some condensers have part numbers on them. MOPAR did put their part number on some vacuum cannister, but AL did not. Breaker plates, point, and housing do not, though they do have assigned part numbers in the books. You also have to cross reference to Service Manuals to isolate what the mechanical and vacuum advance rates are. That help put the slot length measurement to a max degree and also clarify what vacuum bodies go to what distributors. There might only be 5 vacuum body types (max advance stamped on arm) covering 15 similar distributor numbers and the only difference is a spring type and number of washers. So I can even build a correct vacuum advance.

I just do this for my own enjoyment, so I invested in the manuals. I do document all the variances in the distributors I have bought though. Primarily Big Block Dual point types.

I have picked up undesirable NOS distributors just to harvest NOS parts to build a complete distributor. I build this one with all NOS parts except the housing and shaft which I picked at Carlisle as an incomplete distributor. Back up for my Hemi car.

View attachment 668134 View attachment 668135

I have been writing all the numbers donw that I can find also. I come across them quite often and et them to the FSM or sun card specs, but sometimes I really wonder if the parts are correct. They definitely have been "played with: more than the single points over the years. Interesting the letters on the cam plate are the last of the part number.

 

[HALIFAXHOPS]

Can you shoot me a picture of the AL book cover so I know which one to look for?

 

[Dragon Slayer]

I do not have any record on what my cam stop says underneath, just what it has on top, which is a "E"
I follow your statement on different distributors require different initials based on what their curve is. Funny thing, the FSM doesn't even show a dual point for a 440 in 67.

So I set out tonight to try and figure out some characteristics on my distributor.
I set the initial timing to 0, and rev'd the motor. I got a bit more than the last timing mark on the timing cover, so lets call that 13 degrees of mechanical advance.

I am running a 4326s carb, so I only have the option for carb. vacuum.

With initial timing still at 0, I hooked up the vacuum advance. No change in timing.
Tried to rev the motor, would instantly stumble. Unplugged vacuum advance, rev'd fine.

Pushed initial timing to 12 advanced, no vacuum, revs fine. Hook up vacuum, stumbles. Won't actually rev at all from idle.

Pushed initial timing to 20-ish, with vacuum, and same result, complete stumble. Keep in mind, this is all done while in neutral.

Dwell is at 38 degrees. Max carb. vacuum was 23 in.

Not sure how the vacuum is causing an issue here. I think I debunked the theory of it over-advancing, since I tested for that by giving the car 0 initial timing. That gave it a lot room to advance if it wanted too.

Keep in mind, with my older distributor, I always ran 12 initial (before hooking up the vacuum advance), as well as the vacuum advance, and the car ran great.

The Cam stops with E on top I have seen have been 383 IBS-4006 cam stops. Should add about 12 degree at distributor which is 24 at crank, so adding about 10 initial should be good. The problem I see in your post besides the vacuum advance is your only getting about 13 at crank. So you may need to validate your numbers. Are you sure mechanical advance not binding?

How is your carb, is the Accelerator pump giving a shot?

I guess if you went back to your single point to clearly isolate the issue to the distributor. Once you know that is the problem you can go from there. You should have about 32-34 degrees total advance when you rev it. Vacuum at cruise would add another 18-20 depending on the number on the arm for about 50 at cruise low load.

You can test your vacuum with a vacuum pump to see that it hold, and rotates breaker plate.

 

[Dragon Slayer]

Can you shoot me a picture of the AL book cover so I know which one to look for?

You have to ask for specific info on years covered and does it have automobile distributors. Some are industrial, some are not fully up to date. I got mine from a Ford guy. Binders can be deceiving.

 

[67 GTX]

The Cam stops with E on top I have seen have been 383 IBS-4006 cam stops. Should add about 12 degree at distributor which is 24 at crank, so adding about 10 initial should be good. The problem I see in your post besides the vacuum advance is your only getting about 13 at crank. So you may need to validate your numbers. Are you sure mechanical advance not binding?

How is your carb, is the Accelerator pump giving a shot?

I guess if you went back to your single point to clearly isolate the issue to the distributor. Once you know that is the problem you can go from there. You should have about 32-34 degrees total advance when you rev it. Vacuum at cruise would add another 18-20 depending on the number on the arm for about 50 at cruise low load.

You can test your vacuum with a vacuum pump to see that it hold, and rotates breaker plate.

Well doesn’t the FSM say about 12 ish on the crank? Can you please explain more of 12 at distributor is 24 at crank?

I took that to mean if I get that, plus 12 initial, along with whatever vacuum gives me should put me in that above 30 total advance when driving?

I will run the car and hook the vacuum advance up to a vacuum pump and pull on it and see what the timing/engine does.

The carb was rebuilt a few years ago. When the vacuum advance isn’t connected, and I hit the throttle, there is no stumble. So, I believe the accelerator pump is ok.

 

[miller]

Only thing I don't have to spec, is my spark plugs. I have a set of 12s in it now, but the car calls for 11s (which I will install).

Guess you know gap for the plugs is .032. 11s are pretty hard to find these days, 12s a little easier. Funny thing is, from book to book, by the years, when 11s can't be found, one says go to 10s, other to 12s.
Your not running resistor plugs, or wires are you?

 

[Dragon Slayer]

Well doesn’t the FSM say about 12 ish on the crank? Can you please explain more of 12 at distributor is 24 at crank?

I took that to mean if I get that, plus 12 initial, along with whatever vacuum gives me should put me in that above 30 total advance when driving?

I will run the car and hook the vacuum advance up to a vacuum pump and pull on it and see what the timing/engine does.

The carb was rebuilt a few years ago. When the vacuum advance isn’t connected, and I hit the throttle, there is no stumble. So, I believe the accelerator pump is ok.

Distributor turns half the speed of the crank. So when the FSM or Prestolite manual gives you distributor data like 10 degree distributor mechanical advance and 10 degrees vacuum advance, you have to double it to get what you will read on the crankshaft balancer.

Yes initial timing is always given as a crankshaft value. So a 67 car without any emission requirement you would set Initial timing at 12 degree BTDC as read on the crankshaft balance timing mark. The Slot on your cam would add 10 degrees of mechanical advance on the distributor, but this gives 20 degrees at the crankshaft for a total of about 32 degree advance at high RPM and load. When you cruise at high RPM you have lower load and vacuum goes up, so now that vacuum cannister adds and additional 20 degrees on the crankshaft that can push your total advance to about 52 degrees which is about right for cruising and better MPG. Under heavy load like accelerating the vacuum goes down and the vacuum advance goes down so your more around the 32-34 degrees total advance.

Race motor has no vacuum advance normally, and they want the total advance in early and at about 30-34 degrees on the crankshaft.

SO you should be seeing about 30-34 degrees advance total when you rev the motor up around 3000rpm with vacuum disconnected. If your only seeing 15degree max with 10-12 initial, your mechanical advance is not working. A lot of guys put a ball bearing in the vacuum line to plug it and run without vacuum.

Sounds like it runs fine (on the road) without vacuum attached?? If so, maybe the spring and washer comb is not right and vacuum cannister is adding too much advance even at lower vacuum? But you should be able to see that timing increase when you measure timing.

 

[67 GTX]

Guess you know gap for the plugs is .032. 11s are pretty hard to find these days, 12s a little easier. Funny thing is, from book to book, by the years, when 11s can't be found, one says go to 10s, other to 12s.
Your not running resistor plugs, or wires are you?

Yep, I am running the stock recommended gap. I've found the same thing on going to 10s or 12s depending on what you read.
I can't remember exactly if my plugs are resistor or not. Would it matter here? I am running the stock reproduction wires.

Distributor turns half the speed of the crank. So when the FSM or Prestolite manual gives you distributor data like 10 degree distributor mechanical advance and 10 degrees vacuum advance, you have to double it to get what you will read on the crankshaft balancer.

Yes initial timing is always given as a crankshaft value. So a 67 car without any emission requirement you would set Initial timing at 12 degree BTDC as read on the crankshaft balance timing mark. The Slot on your cam would add 10 degrees of mechanical advance on the distributor, but this gives 20 degrees at the crankshaft for a total of about 32 degree advance at high RPM and load. When you cruise at high RPM you have lower load and vacuum goes up, so now that vacuum cannister adds and additional 20 degrees on the crankshaft that can push your total advance to about 52 degrees which is about right for cruising and better MPG. Under heavy load like accelerating the vacuum goes down and the vacuum advance goes down so your more around the 32-34 degrees total advance.

Race motor has no vacuum advance normally, and they want the total advance in early and at about 30-34 degrees on the crankshaft.

SO you should be seeing about 30-34 degrees advance total when you rev the motor up around 3000rpm with vacuum disconnected. If your only seeing 15degree max with 10-12 initial, your mechanical advance is not working. A lot of guys put a ball bearing in the vacuum line to plug it and run without vacuum.

Sounds like it runs fine (on the road) without vacuum attached?? If so, maybe the spring and washer comb is not right and vacuum cannister is adding too much advance even at lower vacuum? But you should be able to see that timing increase when you measure timing.

Ah, I see what you are saying. So then when I set it to zero intial, no vacuum, and rev'd the motor, the mark on the timing cover should've well left the mark? Top mark is roughly 12.5, so it should've left the timing cover marks.

It runs ok, not great right now, with the vacuum plugged.

My carb, 4326s, only has a carb vacuum port, not manifold. So I would never be able to reach the 50 degree advance, since it increases with rpm. It doesn't drop off as I rev.

Tonight I tried to determine if the issue was electrical. Since the vacuum moves the top plate, this doesn’t happen under mechanical advance.

I hooked my vacuum advance up to a handheld pump, and placed a vacuum on it. I watched the top plate move freely. I also checked the wires to make sure they weren’t pinching under advance. Everything looked fine.

I checked the resistance of the top plate itself, to make sure the grounding strap wasn’t shorting out at some point in its travel.

I also checked the wire going to the coil under the same circumstances, comparing the resistance to when there’s no vacuum advance, to when I induce some. In both cases, the resistance stayed the same.

I then ran the car, and using the handheld vacuum pump, I found that the car would start dying at around 13-15 in hg (carb vacuum). I am stumped at this point, since I believe I checked everything that I could.

 

[Dragon Slayer]

I would start at beginning and make sure car is at TDC and distributor rotor is pointing at plug #1. Verify you have plug wires in cap in the correct firing order.

Do you have access to a timing light with built in advance dial. It allows you to rev engine up and use the dial to adjust the timing light to bring the balancer timing mark back to the indictor and then you read the dial to see how much advance you have at high rpm. Your initial plus mechanical advance should give you about 30-32 degree at high rpm. All this with Vacuum line plugged.

You also may have an issue with a worn cam stop lobes. Dwell is the amount of time the "points" are closed. You should be able to get the dwell with the recommended points gap. You are not suppose to gap them outside the recommendation to get the dwell in spec. That normally means the cam lobe is worn.

At low RPM idle you could reading time that you set. Do 0 or 5 degrees. Then apply your vacuum pump to the cannister and start increasing vacuum while reading the timing advance. Some where around 12-14in of vacuum you should have a maximum advance of 16 to 20 degree at the crankshaft. Gradual increase of advance once you get to about 3 to 5in hg.

Sounds like your vac advance works, the question is how much timing is it putting in. Again the adjustable timing light makes this easier.
What is the dwell both points if you set both points to the correct gap?

If you go back to the Chrysler distrib and everything works, you know for sure it is the dual point; maybe it is worn out. I know you do not want to take apart again, but if you do, the shaft should be a 1039LD and the bottom of cam stop should have LD for your IBS-4006Z.

 

[miller]

I can't remember exactly if my plugs are resistor or not. Would it matter here?

Resistor plugs, and wires, were developed to use with electronic distributors, using the wider gap plugs. Such as on Champion plugs, the # starts with R (resistor type). Resistor plug wires use non-wire cores.
Your using dual points, so normally you use wire core spark plug wires, copper or stainless steel. Champion plugs such as J12YC, no R in front, the C at the end means copper core, on our big block Mopars, with point ignition.

 

[miller]

I then ran the car, and using the handheld vacuum pump, I found that the car would start dying at around 13-15 in hg (carb vacuum).

Using the right carb vacuum? Usually two at the carb base, one full, one ported, looking from the front, ported would be on the right side (Carter/Eddy). That's the one to use. Any chance of a vacuum leak?

Dragon Slayer is right, on things to check. Sore subject, but points gap/dwell, for that distributor, should be in the book. If it's not working with the right numbers, something is worn, not letting it act right. Basics, cam and following blocks. See any wear?