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Discussion Starter · #1 ·
Ok I got my MSD vacuum advance today that I talked about in the overheating thread, installed it and I left the intial at 16° then plug in the can and it's reading 29° so I'm assuming that's to much I remembered someone in the thread said to set initial at 10°, the can said it's good for about 10°. I didn't have time for a drive and I forgot to check total advance but before the can I thought that I had 45° @ 2500 rpm. Any advice would be much appreciated.
 

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Discussion Starter · #2 ·
Here's something else I hope won't be a problem, when I went to use the snap ring pliers a piece of one of the eight reducters I guess they're called broke off and there was rust on both sides so it's been cracked for a while, the car runs fine so hopefully it won't affect anything. At least I got the piece before it fell off while things were rotating. I haven't called MSD yet but does anyone know if I can replace that pickup wheel or do I have to replace the distributor?
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Ok I got my MSD vacuum advance today that I talked about in the overheating thread, installed it and I left the intial at 16° then plug in the can and it's reading 29° so I'm assuming that's to much I remembered someone in the thread said to set initial at 10°, the can said it's good for about 10°. I didn't have time for a drive and I forgot to check total advance but before the can I thought that I had 45° @ 2500 rpm. Any advice would be much appreciated.
Yep, too much Initial. 29-16=13. So the vacuum can gives you 13 degrees of advance.


You only want about 20-21 Initial. So, 21-13=8 Try 8 degrees with no can. Then connect the vacuum can and your Initial should jump to 21.


Disregard vacuum advance when figuring total mechanical advance - 8 degrees plus ? to give you around 34-36 @ 2500-2800 RPM's. When you reconnect the vacuum advance, it will add 13 more degrees ONLY at no throttle - ie engine vacuum is at its highest. It will vary as the throttle varies. So at 2,500 RPM, Total mechanical is 36, you let off the gas, timing is now Total (36) plus Vacuum (13) and Full Timing is 49 degrees. Give it part throttle (RPM's must be over 2,500 RPM's) and engine vacuum drops and the vacuum advance also drop proportionately - let's say it now only gives you 7 degrees of additional advance. Squeeze the pedal back to the floor, engine vacuum goes to near zero and vacuum advance now drops as well, lets say 0. Timing is now running on mechanical only, or 36 degrees again. Let off the gas, engine vacuum shoots up and vacuum advance adds the 13 degrees again. The vacuum advance is constantly varying based on throttle position which means engine vacuum amount is also varying.


With no load or light load on the engine, the timing will increase up to 13 degrees regardless of what the mechanical advance is, whether it be under 2,500 RPM's and only at 28 degrees mechanical, or idle and 8 degrees. So the vacuum advance has a range of 0-13 degrees on top of whatever the mechanical advance at that RPM is at that time. The addition of the vacuum advance under no or light throttle is what helps to cool the engine and improve gas mileage.


Anything above 2,500 will always be 36 degrees, because that is the RPM you have reached Total mechanical advance - but it will vary between your Initial 8 degrees at idle (650 RPM?) and Total of 36 degrees @ 2,500 RPM's. This spread from 8 to 36 is called your Timing Curve (mechanical) which you could actually plot on a graph showing RPM and the mechanical timing at that RPM - up to 2,500 RPM's (or 2,800 RPM, or 3,000 RPM, or 3,500 RPM - where you choose the RPM where you want Total mechanical advance to be all in at).
 

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Discussion Starter · #5 ·
Ok sounds good, and thanks for the great explanation again, I'll set it up like that...idk why I wrote down 45° @ 2500 it was a while ago and maybe it was learning how to use my new digital timing light but I have notes from talking to Butler that say 34-36° at 2500 just like you said. What do you think of the piece that broke off the distributor, going to be a problem, ever seen that before??
 

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Your distributor is toast. It won’t work very well if at all with a missing pole piece for the magnetic Hall effect switch. It may fire six or seven cylinders at best. I would not even put that in the engine.

36 Total is good I still recommend the vacumn setup I previously outlined for you getting max 10 Degrees on vac advance. Those adjustable cans always have too much. Yes it is only 3 degrees too much but still too much.

36 + 10 vacumn....and check for pinging..if so dial base back in 2 degree increments until pinging stops stay there.
 

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Maybe there is enough left on top to grab a signal. But if more breaks more problems. You don’t need the most expensive distributor to run great. Just needs to be setup right
 

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Discussion Starter · #8 ·
Well it was running good in the garage which I was surprised so maybe there's enough left we'll see, this can isn't an adjustable so I'll set it like recommended and go from there....it's always something, hopefully it makes it through the summer and maybe Santa can bring me a new distributor 👍
 

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Discussion Starter · #11 ·
Well I didn't see it in any descriptions and no directions or allen wrench included but I can research it some more also I can get a reluctor gear for 20.00 just need press a new one on...maybe a winter project.
 

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Got it. You may want to read this
 

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Discussion Starter · #13 ·
Ok finally got to timing this thing after waiting for some braided hose and fittings, so off the can I set it 8° initial, plugged into the can I'm at 22° so I'm getting 14° out of the vacuum advance...sounds good stabbing it to the floor from idle no hesitation just one pop through the carb the first time I did that but never again. Don't have time for a test flight today but for sure this weekend. How does that sound to everyone?
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Discussion Starter · #14 ·
Also got a new reluctor gear but so far this one is working, hopefully I can make it a winter project and I don't end up on a flatbed this summer 👍
 

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Also got a new reluctor gear but so far this one is working, hopefully I can make it a winter project and I don't end up on a flatbed this summer 👍
Sounds like a good start. You at least know what the can is adding.

Are you using a dial-back timing light or a degreed balancer - my brain can't recall? In any case, the above posts can be followed in figuring your total.

22 can be good. Just make sure it does not start/labor hard in spinning over the engine when hot, but you should be fine.

So 8 + 22 is essentially your Initial with the can hooded up to direct manifold vacuum.

What is needed now is to know (with vacuum can disconnected) what is your Total Mechanical Advance 8 + Distributor Advance (weights) =? AND at what RPM the Total Mechanical Advance (TMA) stops.

A good number I like to start with is 32 degrees TMA (you can use 34/36 as well, I just am conservative at first). So, if you know the Initial is 8 degrees with can disconnected, to get 32 TMA, 32 - 8 = 24 degrees needed from the distributor weights.

If you get 24 degrees out of the distributor weights, keep in mind that you will need to advance (rotate) the distributor to get either 34 or 36 degrees TMA. When you do this, you also advance your Initial (no vacuum can) a like number of degrees. So for each 2 degrees of TMA, you will add 2 degrees to the Initial, ie 8 + 2 (34 TMA) = 10 degrees Initial, or 8 + 4 (36 TMA) = 12 degrees Initial. Now to this you will add the 14 degrees advance from the can when you reconnect the vacuum line, so 10 + 14 = 24 degrees Initial, and 12 + 14 = 26 degrees Initial. This could be TOO MUCH and you can have problems with detonation. You can try it, take it for a test ride with the vacuum line disconnected to see if the engine likes 12/14 degrees. Then hook up the vacuum line and test again, but if issues with the can hooked up but the engine responded well to 12/14 degrees Initial, keep the Initial of 12/14 degrees and hook your vacuum line to a Ported nipple on your carb. You should have one of these on the carb.

With a Ported source, the engine vacuum will not pull in the can at Idle as it does from direct manifold vacuum. You may get some vacuum pulling a slight amount from the can, but it won't be much. The difference between ported and direct is that the can won't be pulled in at idle, but it will still work once going down the road. But here is the thing, without the vacuum can hooked to direct manifold vacuum and bumping the Initial 8 degrees to 22 degrees, you may not get the benefits of engine cooling at idle speeds. So kind of a catch 22 here.

The solution could also be to get a vacuum can that only provides 10 degrees additional advance OR adding a stop/limiter to the vacuum advance arm that pulls in on the distributor so it will only pull in 10 degrees. But I won't get into that as that may add more things to consider and confuse. So play around with what you have and report back. If the carb backfires again, it could be that you do need more than 8 degrees of advance. Just stay away from any Detonation during wide open throttle or pulling a hill with the engine lugging. Just back out of the gas pedal and bring it home for more adjusting.
 

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Discussion Starter · #16 ·
Got it, I wanted to check the total without the can but forgot and put the vacuum line back on and had to leave, I do have the curve Butler set up but I need a road test. I'm surprised the can gave me 14° was reading that it would be 10° I'm running about 9.4 compression with one step colder plugs than Butler provided and always use 93 octane so maybe I can run 10° initial we'll see.
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Discussion Starter · #17 ·
Sorry forgot to answer you on the timing light, it's a newer Novus digital that you tune the degrees up and down and watch for the zero marks to line up, is that what you consider a dial back light?
 

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Sorry forgot to answer you on the timing light, it's a newer Novus digital that you tune the degrees up and down and watch for the zero marks to line up, is that what you consider a dial back light?
That's the one I bought... It doesnt play well with CDI boxes. Still waiting to try it with a remote power source.
 

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Discussion Starter · #19 ·
No CDI on mine, so bumped the initial timing to 10° no can, plugged in the can and reading about 24-25° mashed the throttle to the floor about six times from an 800rpm idle with no hesitation or backfire. So there was a 10 yard pile of mulch in the way of getting the car out for a test flight so that's gone today and now it's raining on and off of course so stay tuned for an update. Also want to check my idle mixture after all this.
 

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No CDI on mine, so bumped the initial timing to 10° no can, plugged in the can and reading about 24-25° mashed the throttle to the floor about six times from an 800rpm idle with no hesitation or backfire. So there was a 10 yard pile of mulch in the way of getting the car out for a test flight so that's gone today and now it's raining on and off of course so stay tuned for an update. Also want to check my idle mixture after all this.
How the car acts sitting in your driveway tells you very little about how it will act driving under load.

Looking back at the chart you posted a few iterations back, with 10 initial in order to get to where your engine's "happy place" probably is you'd want to be using the silver advance stop bushing, which according to the chart allows 25 degrees of travel. 25+10=35, and that's usually a reasonable setting for "most" Pontiacs. 67 and earlier closed chamber heads tend to like more than that, some aftermarket heads with "good" chambers like a little less, but 35 is a good starting point.

Bear
 
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