Seems like you're still hooked to manifold vacuum.

On the Carter you have, (Edelbrocks, too) the ported nipple on the lower left side of the carb - when you're looking at it head on - is ported. The right side nipple - again looking head on - is manifold vacuum. If you peek at both, you'll see the one on the right is lower - below the venturi while the left one is above. The 3/8" nipple in the middle is manifold vacuum for the PCV. There's another one in the back (I think) for power brake booster vacuum....or whatever you desire.

Get back to us with the situation rectified (?) and we'll talk timing some more.

 

The lower left is definitely the one I'm using. I bought an Innova Pro tonight to help. I should have it Friday to help see the advance and what rpm the timing tops out at.

 

I installed an HEI with vacuum advance on my 1970 460, reasonably priced and works well.

 

First off a few myths.....
Vacuum advance serves one purpose. Better economy at cruising speed.
It is NOT essential (sure it's nice to have hooked up, but for tuning purposes, just keep it capped off until you can get everything running right. Tune it AFTER everything else is set properly).
Manifold vacuum making an engine run better is a bandaid for an improper curve. Get the curve correct FIRST.

Second, there is nothing wrong with an MSD distributor.
In your case, you needed to run the black bushing which is 18 degrees of advance added to the initial. A safe initial at that point would have been 18. This would have put you at 36 total. 16initial and 34 total would have been safe too, but you said it ran better with more initial. You could have tinkered around later to find perfection, but that is a good safe setting.
I would have gotten the springs to where full advance came in around 2800-3000.

I didn't see where you were checking for total advance with that distributor. Chances are, when you had the ignition set at 22, the stock bushing was in the distributor and your total was through the roof. They normally ship the MSD with the red bushing and the heaviest springs. The red adds 28 degrees of mechanical advance, so your total would have been 50 degrees. This would be the source of your knock/detonation. With the stock springs the total would have come in at 4,000 rpms probably, but you changed them out and the advance was coming in early, the engine would have been weak and prone to detonation under even light loads.

All that said, I mostly use Durasparks, even on my high performance engines as I am not scared of welding up the advance arm and taking the distributor apart 5 times to get my curve correct. I've never messed with the GM hei, but I just wanted to toss out my opinion on the above MSD issue.

Drew

 

I appreciate all of the input. I'm still messing around with this. One question that no one has answered is what timing should I have at idle with vacuum advance? It was mentioned that both 39 and 33 were too high.

 

39 and 33 degrees BTDC at idle is way way too high. The engine won't tolerate but about 34-35 degrees BTDC maximum advance under wide ope throttle.

 

Timing at idle should be ~ 12* BTDC. If you're running ported advance, which you are at the moment, yes?.... there should be 0 - zero vacuum advance at idle.

Your 33* - 39* BTDC is too high of an initial/static/base timing.

 

My bad....fergot about your cam setup.

Initial timing should be anywhere from 16* - 18* BTDC with your cam's lift and duration....presupposing the cam timing was set at the "straight up" position.

Hehehe...it's been a while, JKessler00. I can't remember what I had for supper two hours ago let alone what your engine has for innards.

Back to square 1, am I?

 

I guess everything I thought I was starting to understand is out of whack. I thought the whole idea of vacuum advance was to raise timing at idle for better efficiency and cooling and to raise the rpm's so that you don't have to have the idle screw set to have the throttle plate open very far? So if there's no vacuum at idle, what good is the vacuum advance? I'm going to be wasting a lot of time and risking engine damage if I'm messing with this without a good understanding of what I'm doing.

 

the purpose of vacuum advance is to change the position in the cycle where the plug fires. It takes a fixed amount of time for the current to travel down the wire and fire the plug. The explosion takes a certain period of time to happen. As the engine turns faster, the firing has to occur earlier in the cycle

so, when you're at idle speed, the firing has to start at 8 degrees before TDC. But when the engine is spinning faster, say 2000 rpm, the firing needs to happen sooner, maybe 20 degrees. At WOT, the firing needs to happen even sooner-perhaps 35 degrees

the weights in the distributor "fly out" as it spins faster-that's mechanical advance. Vacuum advance, usually ported, causes the interior of the distributor to rotate, or advance, to advance the timing. In a WOT condition, there is no vacuum, so mechanical advance takes over

basically, the advance causes the plugs to fire earlier, making the explosion happen at the most efficient place in the rotation

 

First off, there's no reason to think you're risking any kind of engine damage - you're not......you're not even close to risking any damage.

No, your thinking isn't out of whack, just somewhat...incomplete. There's two scenarios in the vacuum advance application...one is manifold vacuum advance, the other is ported or timed/spark vacuum advance.

That is one scenario...and you're talking manifold vacuum advance here. Hooking the distributor to manifold vacuum advance does raise the timing, does give better efficiency to some degree, does let the engine run cooler to some degree and does increase engine RPMs at idle. One still has to have the carb's throttle plates set such that they're not open to the transition slot more than 0.020"....or such that they form a "square." One has to adjust the carb - curb idle speed and mixture, as well as timing in the same manner whether running manifold or ported advance.

That's the second scenario....ported, or timed vacuum advance. Waaay back in the day, distributor vacuum advance was hooked to manifold vacuum....no "ported" vacuum was to be found. Hence the phrase of disconnecting and plugging the distributor's vac adv line when timing a vehicle, which sticks around to this day, even though ported has no vacuum at idle. At idle, all you have is base timing, set at whatever makes your engine happy. Mechanical advance is what's already built in to the distributor - the weights. These two together make up your "total timing." Ported vacuum advance comes in under load....and is "load
related." Mechanical advance is "RPM related."

There's more, but I've already written a book here.

To be continued.........?

 

I was digging around earlier and realized I could use my brake bleeder to measure the vacuum on each port of the carb. When I finished tinkering Friday, I had an initial timing of 13*. I could not get the truck started today (much colder out too) without turning the idle screw almost 1 1/2 turns. I did this to keep it running so I could measure vacuum, knowing that I couldn't keep it like this because I'd have run-on. The port I'm using on the Carter carb (left side) measures 12" at idle (albeit a little higher idle). The right side is 15". So neither are ported or something else is goofy. In the 15 minutes tops that I was out there today, I could see steam coming from the breather. I peeked inside at the temp gauge and she was overheating. At that exact moment, coolant starting surging from the radiator so I immediately shut down and left it at that. With my advance connected to the port giving 12", it runs cool as can be (at about 31* and idle screw backed way off).
The way I see it, I need to set the total timing at ~36* (when mechanical is maxed) and tighten the distributor down. I'm guessing when I do so, my initial will be really low. So do I then leave my vacuum connected where it is and adjust my vacuum can to boost me to 18* at idle? 18* seems to be what she wants.

 

Something is wrong with having vacuum at idle while connected to the ported nipple. I think the curb idle screw is down too much, opening the throttle plates such that the transition slots are showing more.....engaging the main circuit.

With the cam you're running, I would set the initial at ~18* BTDC. No vacuum to the distributor, of course. Back off the curb idle and set the mixture with a vacuum gauge. Re-connect the vacuum to ported and check the timing again.

Run the vehicle with the vac can's adjustment all the way CW (earliest/most vacuum signal). Listen for any "pinging" at various loads....medium cruise to WOT, freeway cruise then punch it, high gear up an incline, etc. Back off (CCW) the can's screw a turn or two if you hear pinging. Test run again/adjust 'till you hear little or no pinging then turn the can's adjuster CW 90*.

Another thing - don't get too overly concerned with the timing numbers. There's a lot of yakety-yak about this being right, that being wrong, etc. There's leeway involved and the numbers are not always a dead-nuts thing for perfection. You wouldn't believe what some engines like....hehe...and that's the name of the game.

 

Alright, a little progress... Initial timing is set at about 17*. (The slightest movement seems to jump it over or under 18 so I settled at 17*.) I was able to back the idle screw off a ways because of this and guess what, no vacuum from the port on my carb!

I found an article that mentioned hooking a vacuum gauge up to the manifold and watching the numbers as you set the idle mixture. Unfortunately, the vacuum didn't seem to change, no matter how much I turned the screw in either direction. Right now, I have them both at 1 1/2 turns out.

Before going for a spin, I revved it a little from idle. It sounds good. If I pop it quick to the floor, it backfires through the carb. I don't feel like it's timing unless the vacuum advance would give it too much with a quick pop? I also read an article where a guy stated that once you get a good pop through the carb, they're never the same. Any truth to that?

 

not any more. In the past, it was possible to blow-out the power valve, but the carburetors have been redesigned, and that no longer occurs

http://www.enginebuildermag.com/2013/01/the-truth-about-power-valves-used-with-holley-carburetors/

i did have a backfire blow out the check valve in the brake booster, however that caused a severe loss of vacuum!