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Timing/Ignition questions.
#1
I have a couple of questions regarding my ignition system, and I'm hoping you guys can help. I just got a new timing gun the other day and am waiting for a new carb to arrive in the mail so I can set the timing..I've watched a ton of videos on YouTube, I think I understand what to do...however I'm not really sure about the exact components in my mustang. Not sure if I have "points" or electronic ignition? And is this "full vacuum advance"? 
[Image: IMG_3172.jpg]


[Image: IMG_3169.jpg]

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Also, when I'm shooting the timing gun this is what I aim at I believe. However, I crawled under and took a good look and I didn't see any marks or degree indications to tell me how close to TDC I am?
[Image: IMG_3171.jpg]
Any comments/suggestions would be greatly appreciated!


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#2
Firstly your distributor is the standard Autolite/Motorcraft distributor fitted with an electronic conversion kit by the looks of it an Accel unit as it has the spark controller on the outside unlike the Pertronix which is all inside the distributor. While your at it check the distributor shaft for excess wear as this can cause all types of problems. The shaft should have minimal movement and if excessive replace the bush and check the shaft for wear, but shafts usually hold up and the bush gets flogged out. 
You are correct in where to read the ignition timing on the harmonic balancer. The triangular piece is where you line up the marks on the balancer with. There will be numbers inscribed into the balancer that read 10 (ATDC) 0 10,20,30 etc (BTDC) with lines in between. They're hard to read so marking with a thin paint pen works best or liquid paper/white out is also good at the timing you want run at idle, around 12-16 degrees BTDC works best with the Cleveland. You'll also want to find out what the total advance is. Do this by revving the engine up until the timing marks go no further, being a standare type distributor it should be around 20 degrees of mechanical advance. Also the vacuum advance needs to be disconnected and the vacuum source plugged. So total timing is the amount the distributor advances at a certain RPM where it can go no further. Another to check is to make sure you balancer isn't "spinning" by where the rubber bonding strip between the inner and outer hubs is worn and causes the outer hub to spin on the inner hub during revs. If that happens you'll need to replace the balancer.  
There's obviously something I would've missed in your question which somebody will chime in to provide, but that the basics of what you have and what needs to be done. Good luck with and let us know how you go with it.
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#3
Your ignition is an aftermarket electronic ignition made by Accel. It has a single vacuum advance, which is the small metal can on the side of the distributor with the rubber hose attached to it.

You have the right location for timing it and have located the timing pointer. The timing marks are not always easy to find. It seems like they are always on the wrong side. You'll have to either turn the engine by hand, with a breaker bar and socket on the nut at the end of the crankshaft and in the middle of the crank pulleys where you can't see them, or bump the starter over with a remote starter switch, attached to the solenoid, until you can see the timing marks. If they're not clearly marked you'll need to mark them with a contrasting color marker, usually a white or black pen or paint.


“If you can't explain it simply, you don't understand it well enough.”
--Albert Einstein
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#4
I'll have to look a little closer in the morning with some additional light. I do have a couple paint sticks around to highlight any markings I see.

BTDC stands for BEFORE top dead center right? If I set it to a degree of BTDC, doesn't that mean it will ignight before finishing the compression stroke? I thought you wanted ignition to happen just after TDC when the piston is going down. ?


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#5
You actually want maximum cylinder pressure right after TDC. It takes a few micro-seconds for the spark and complete combustion to occur. Therefore, initial timing needs to be somewhere between 6°, or so , and around 16° BTDC. Because the delay time until complete combustion and maximum cylinder pressure is fairly constant the ignition has to advance even further as the engine speed increases, which means the total advance will be around 34° to 38° at 2,500 to 3,000 RPM. These are general values and engine type and build will determine actual timing advance.


“If you can't explain it simply, you don't understand it well enough.”
--Albert Einstein
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#6
(03-20-2017, 01:03 AM)Don C Wrote: You actually want maximum cylinder pressure right after TDC. It takes a few micro-seconds for the spark and complete combustion to occur. Therefore, initial timing needs to be somewhere between 6°, or so , and around 16° BTDC. Because the delay time until complete combustion and maximum cylinder pressure is fairly constant the ignition has to advance even further as the engine speed increases, which means the total advance will be around 34° to 38° at 2,500 to 3,000 RPM. These are general values and engine type and build will determine actual timing advance.

That has to be the best explanation of the spark/compression/timing process I've ever read.  Thank you for that.  thumb
Eric

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#7
Thanks for the additional info. All my parts are supposed to be arriving today! So I'm cleaning out the gas lines and getting fresh gas in there...just changed the oil. Hopefully I'll have good news later today!!


My carbon footprint is exceptionally large.
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#8
Manifold vacuum at the carb will always be below the throttle plates and ported vacuum will always be above, though some carbs do seem to have internal channels. If ports are side by side, then with one uncapped at idle isn't sucking air it is ported.
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#9
(03-20-2017, 04:04 PM)Jeff73Mach1 Wrote: Manifold vacuum at the carb will always be below the throttle plates and ported vacuum will always be above, though some carbs do seem to have internal channels.  If ports are side by side, then with one uncapped at idle isn't sucking air it is ported.

So what is the difference between manifold vac and ported vac? As mine currently sits, the vacuum line coming out of the distributor goes into a port on the intake manifold. (Edelbrock performer intake) Should I just keep it like that and plug the two small ports on the front of the carb?


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#10
(03-20-2017, 09:53 PM)Fredensborg Wrote:
(03-20-2017, 04:04 PM)Jeff73Mach1 Wrote: Manifold vacuum at the carb will always be below the throttle plates and ported vacuum will always be above, though some carbs do seem to have internal channels.  If ports are side by side, then with one uncapped at idle isn't sucking air it is ported.

So what is the difference between manifold vac and ported vac? As mine currently sits, the vacuum line coming out of the distributor goes into a port on the intake manifold. (Edelbrock performer intake) Should I just keep it like that and plug the two small ports on the front of the carb?

Ported vac gives you zero vac advance at idle and as you increase rpm (throttle blades open) the vac advance is applied.  With manifold vac you have vac advance as soon as you start the car.  Initial timing on the motor is without adv that is why you remove the vac line to the distributor when timing the motor.  Ported vac was designed because of emission controls in the late 72 and 73 models.  With your current setup you are using manifold vacumm.  It all depends on your motor which type you use, I use ported vac but I  am also using an TBI system on my car.  I see the subject on which type of adv to use debated all the time, just see which one works best for you.
-john

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-john
(jbojo)
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