You stated early on in this thread that you are willing to learn, and you've certainly proved that throughout the previous 874,252 posts in this thread. LOL

Keep posting the details no matter how trivial you think they are.

Starting with the easy stuff first, the bouncing 15'' - 16'' vacuum with a cold engine is normal.

When you have a vacuum gauge installed in your truck, you will actually see how much it changes during different driving conditions, from 0'' at WOT to +/- 25'' during deceleration.

The 18'' steady vacuum when the engine is warmed up, confirms the general guideline of ''do this and do that when the engine is warm''.

Generally speaking, when someone says their engine has 18'' vacuum at idle, it isn't as helpful as when they say they have 18'' of vacuum at 800 rpms with 14* ignition timing and vacuum advance disconnected.

The vacuum reading is part of a relationship.

For example, you have already seen vacuum increase with an increase in timing. (Manually advancing the dizzy by hand.)

You just saw the vacuum increase with an increase in rpms.
(17'' at 800rpms the other day, and 18'' at 900 rpms yesterday.)

So, at present, we are not actually comparing apples with apples.

May I suggest that we start from scratch, and do all observations in one go.

With the engine warm :

1
Disconnect the vacuum advance, and make sure both manifold and ported ports are plugged good 'n solid.

What is the vacuum, idle timing and rpms ?

2
Connect the ported vacuum advance.

What is the vacuum, idle timing and rpms ?

( 1 and 2 may or may not be exactly the same.)

3.
Plug the ported port, and connect the vacuum advance to the manifold port.

What is the vacuum, idle timing and rpms ?

This is the only time that you should see a significant increase in the vacuum, idle timing, and rpms.

Make sure that you are using the exact ports as shown :




However, before doing the above suggestion, clarify this :

Ensure that you are not confusing the timed (ported) port with the manifold port. (Maybe a dumb comment, but I have to say it.)

The PCV port is connected to the PCV valve on one of the rocker covers.

The PCV valve is working.

The other rocker cover has either an open breather, or a pipe connected to the air filter.

The brake booster is connected to the power brake port.

That should just leave the tranny connection which is where ? (vacuum tree on the back of the intake manifold ?)

Anything else connected to the tree ?

If only the tranny is connected there, fine, it can be disconnected for the vacuum gauge. (Or left there and use another port on the tree.)

Make sure that all plugged ports are truly plugged.

Use the same intake manifold connection for the vacuum gauge for all 3 observations.

WTF does this have to do with the timing curve ? Haha, it will become apparent soon enough, if not already.

 

Here’s a few comments to conclude my contribution to this thread.

Using one heavy and one light spring, the total timing was all in 500rpms later than advertised.
Using two medium springs, the total timing was also all in 500rpms later than advertised.
That’s a good enough reason to return the MSD 6A ignition controller for repair, refund, or exchange, assuming it’s under warranty.
Plotting a timing curve was not required to observe that problem.
(For those of us who do not have a separate ignition box, but rather a dizzy with a built in ignition controller, the dizzy would be returned.)

Mariahb4q suggested that all one has to do is set the total timing to be all in at a certain rpm, ignore the curve, and let the idle timing be a default amount.
How would we know if the timing curve is what it should be ?
The OP’s timing curves, once observed, were seen to be exactly the same with two different spring settings, which is clearly problematic, and would compound the reason for returning the ignition controller.
Could the supplier, in this case MSD, argue with facts ? No !
The reader can decide if observing and plotting a timing curve is beneficial or not.

She also suggested that checking the timing curve was so stupid, that it is equivalent to making a graph for dialing in a carb.
LOL ! What’s the first thing we do when we fit an AFR gauge ?
We observe the numbers to see if we are running too lean or too rich, during all driving conditions, and adjust the carb accordingly.
Doing that is exactly the same principal as checking the timing curve.
The reader can decide if he/she is clever enough to know what the AFR is whilst cruising at 70mph, without an AFR gauge.
I managed to climb out of my truck and open the hood at that speed once, but because my foot was no longer on the gas pedal, the truck started slowing down, so I wasn’t able to check.

The OP checked and observed that when he advanced the timing, the vacuum increased, and conversely the same.
This is the correct relationship.
He also observed that when he connected manifold vacuum advance, the timing increased by 15 degrees whilst the vacuum remained static.
I can only surmise that the vacuum gauge was inadvertently connected to the ported vacuum port at that time.

The general advice given is to tune an engine to give the highest vacuum reading.
In the OP’s case, he observed +/- 18’’ at +/- 800rpms with ported vacuum.
He should be able to observe +/- 21’’ with manifold vacuum at +/- 800rpms. (It’s a smog free engine, so having a ported vacuum connection is not compulsory.)
21’’ is higher than 18’’, but once again, the reader can decide what he/she wants.

 

I agree the idle vacuum needs to be at 20 or above for a good balanced tune.

 

Good morning 6 by 8. Haven't heard from you in a while. So for the record, I agree with you about plotting a timing curve and here's why. How would I know if the distributor is producing the correct timing curve that it's supposed to if you don't plot the curve? Had I not done that, I would have never known that my timing was coming in 500 rpm later than what MSD says it's supposed to.

The MSD 6a is not under warranty anymore. I've had it for years, but it was on another vehicle at one point in time, then it sat in my garage for a long time until now. So returning it isn't an option. I haven't swapped it for the one in the truck yet, as I got distracted by another one of my vehicle projects, while at the same time, waiting for a response from MSD. But that looks like that isn't going to happen since it's been weeks since I emailed them. I guess I could send the same email to Summit, since I did get a response from them on another question.

I had a thought (yeah I know; uh oh, he's trying to think...LOL). So although the spring combination we've been using is making our all-in rpms come in later that what MSD says they will, the lighter spring combo did come in earlier than the heavier spring combo, regardless of where they came in at. With that said, maybe we can try a 1 medium and 1 light spring and see what it comes in at; shooting for 2500 rpm??? But by doing that, from past experience so far, I'll have to retard the timing so it won't ping. So I'm assuming if I swap the springs to lighter ones and we get the rpms to come in at 2500, I'll probably be somewhere in the neighborhood of 8*-10* of initial timing, which also lowers the vacuum the more retarded the timing is. Which leads to my next question below.....

It's ironic you revived this thread today because just last night while I was laying in bed counting sheep trying to get to sleep, the thought crossed my mind that I don't think (or I don't remember) anyone answering my hypothetical scenario question regarding which would be the better setting for overall engine performance & power; 14* initial timing & all in at 3500 rpms or 10* (or even 8*) initial timing & all in at 2500 rpms and all other factors being the same, such as total mechanical timing. Do the engine rpms rev quicker and have more power with more advanced initial timing and a later (numerically higher) all-in rpm or with more retarded timing with a quicker (numerically lower) all-in rpm? The answer to this question should determine if it would be a waste of time to get the all-in rpms down to 2500 or not. If my memory serves me correctly, when I was using the 2 heavy springs and the rpms came in later, my initial thought when I test drove the Bronco was it seems a little sluggish.

So how's your mom doing? Are you still letting her play with cords? LOL

 

On a stock engine you're better off having it all in at 2500 as long as it's not pinging.


As far as your vacuum goes you're worrying about it too much. set your timing where it needs to be and the vacuum will be what it's going to be, as long as it's in the acceptable range which yours is then set your idle mix as best you can and drive. if you want to do some weights and springs work you can to get your curve where more initial is possible and you're still all in at 2500. but unless you enjoy doing that why bother.

I have performance engines that won't pull more than 11 inches and the power brakes work fine and I don't care.

 

Good point. It's been said that I want a higher vacuum reading, but I don't think anyone has ever explained "why".

So maybe I'll try setting it up to where the rpms come in at 2500 (right now it's coming in at 3000) and retard the timing just enough so it won't ping and see how it responds, then go from there. I've been logging down my timing charts so I'll have them to refer to in the future. Maybe I'll try the lighter springs and chart another curve and see what happens. Trial and error, right?

My engine is only mildly modified; higher compression pistons that stock (9.3 - 9.5), RV cam, edelbrock intake & carb, MSD dizzy, ignition box, & coil. I will be adding a set of headers soon. That's about it. So maybe 2500 all-in with retarded timing might work? We'll see.....

 

2500 for timing all in on an engine that is expected to tow is going to be too early, that setting is fine for a car but not in a truck expecting to tow.

 

We're not talking about my truck, we're talking about my Bronco. I don't tow with my Bronco or on the rare occasions I need to, it won't be anything heavy. But while you mentioned it, would all-in at 3000 still be too early on my truck that I tow with? Right now the timing on the truck is all in at 3500.

 

2500 would be better, 3000 will work. 3500 is too high you're losing efficiency for that 1000 rpm. . and how often are you going to be running 3500 anyway ? when passing maybe and that's about it.

On a the tow vehicle 3000 is plenty high. the only real way to know is to use it and listen. with the fuel we have today and the other variables there is no generic number that works for everyone,.

 

Good morning guys:
My head hurts. I began reading through this thread, and finally after trying to digest all of the information here, i have to admit, my head hurts.
I am a "Bob2000" fan. Bob goes into length about setting up a good balance between vacuum and mechanical advance systems and fuel management.
Timing Tips for Ford Distributors (bob2000.com)
Carburetor Tuning the Scientific Way (bob2000.com)

I had to chuckle when you mentioned pulling the trailer up a steep grade and burning holes in 3 pistons.
Yep, that is the results of too lean of a mixture. My 2 cents is at that point if too much advance, then you'd be getting pinging. But, you may not be hearing the detrimental pinging.
Add 2-stroke oil to your fuel when you are headed out and know you'll be climbing a long hard grade while smiling big because you've got those secondaries opened partially while your tach reads 4.500 rpm (or more), and you are out pulling some of those superduties who are up against their governor. hahaha read-em and weep. (i'm dreaming of course, but maybe not). arh arh.
omg, pulling a heavy trailer up the big grade heading east out of Salt Lake City on I-80, in a '95 Suburban diesel 6.5L turbo, it was well over 100-degrees outside, and i climbed the hill (first gear) with my temp stabilized at 255 degrees, and no head gasket issues. Was very scary because that was the one an only time in 15-yrs that the engine temp kept climbing after the fan clutch engaged (@240 normally).
(thought I'd throw that in for the diesel guys).

When installing my 429 (385 series) a good ford mech warned me by saying "if your are running 9:1 compression on pump gas - Good Luck with curing pinging with timing" !!
I am running a Crane flat tapped midrange came and hypertuectic pistons, so nothing fancie-dancie. yep
Yes, my rotating assembly has been balanced for continuous high rpm running. _ _ like a dirt bike !!
Now, i have been through burning holes in pistons back in the early '70's when motorcycle racing.
So, I am not worried about specific numbers, or anything like that, since i've never relied on a timing light.
My old mentor, Dad, a lifelong mech taught me to time an engine by "feel" while behind the wheel. hahaha
Yes, i did what Bob2000 suggested and i played around with distributor weights to lock in total mechanical.
Oh, almost forgot: I chose to run a 3310 Holley 4-bbl carb with manual choke to give the engine lots of fuel for cooling while climbing up from sea-level to 8,500 feet pulling a 21-6 Willie Preadator inboard boat.
No problems, and what my final cure for run-ability was: I'm running no vacuum advance !!
Now, if a techie were to put my engine on a scope he would probably tell me my engine timing is all out of whacker's, butt, if you saw the smile on my face while pulling the grade with my engine happily purring along at 4400 rpms or more constant pull (yes of course my secondaries are open), you might agree with my conclusion. My techhie buddy remined me only mechanical is ok, but your fuel mileage may suffer.
Well, pulling trailer's with 4:10 gearing and no over-drive will not garner any respectable mileage numbers what so ever, and that 3310 Holley is delivering ample fuel, so no worries. guzzle-guzzle hahaha

Off topic for machine, but right on topic for timing / fuel conversation: (what i think interesting).
My 1982 approx. Husky 2100cc timber faller's saw will govern itself by choking (over-fueling) to prevent scalling of the piston from expanding (too tight of clearances again), or lack of fuel (lean mix), and the engine running too hot leading to ? hole in piston, or Siezure until cool-down.
The 1995 Honda Passport powered by an Isuzu 3.2L v-six engine was Factory governed @ 6.800rpms by over-fueling the engine to choke it back and the fuel at the same time cools.

I am sharing this for those new to engine management, and we can go very basic with good results.

My father, who is currently 93yo, reminded me that most engines were timed with a simple Vacuum gauge before the advent of timing lights. Also, my early ****** jeep 4-banger has all mechanical advance because vacuum advance was not offered in 1946 on the flathead 4-cyl engine. Probably lots of gas engine farm tractor ignitions only ran mechanical advance, although they were governed at low rpm's.

You are running 9.5:1, so without a fuel injection computer to trim fuel and change timing, we are working with some constraints. It sounds like you are getting close.
Hope you reach your plateau, and go out and put 20,000 miles on that engine. Have fun doing it.

Len

 

You can cure pinging with the timing but it will come at the cost of performance , that's where octane is the solution.

Jetting is of course a serious matter especially when towing. but it's easy to check just look at a could plugs and you'll know. if you're running a weekend cruiser stay as lean as you can safely, if you're really working the engine stay on the rich side that's what Ford did. if you bought a new pickup in LA or Denver it had the same jetting , so what's that tell you ?