Pulled a mechanical msd out of my 69 recently. Decided to go with the petronix hei with vacuum adv. (Had recently put one in my 68 without any issue's). Started right up with the new dist but on test drive had a pre ignition from hell. Tried retarding several times and many degrees without any change. Manually tested the advance... Never had this issue before. Low miles on a thirty over, nine and a half to one build. Only the best top shelf gas. Does fussing with the advance curve sound like the place to start? Maybe a lighter spring? I know you can adjust a mechanical dist with lighter and heavy springs but is that the case with vac adv dist's as well? Never had to adjust curve before. Maybe it doesn't like hei's and is just spoiled? Any advise or comments are very much appreciated.

Definitely sounds like some tuning of the new distributor is neccesary. What type of MSD distributor did you replace (vac adv, or straight mechanical adv model), and why?

Are you sure you've got it stabbed correctly?

I'd pull it, bring no. 1 to TDC compression and then reinstall with the rotor pointing towards no. 1 cylinder.

Do you have an adjustable timing light? If not get one. Then you can set the timing to total timing, not timing at idle.

It was a mech MSD dist. After about five years the distributor would get all rusty and built up with crap. Plus they're not cheap. Have been running an HEI (vac adv) in my 68 for longer than that without any issues. I put another in it recently because it's a shoestring build compared to the 69 and I was pleasantly surprised on it's performance.
I was kind of thinking the same thing Dr. (after nothing else was working). Usually careful about those things but you never know. It does purr at idle and only start the ping at about 2500 rpm. Since I tried timing points from nine down to about three degrees, wouldn't I get it right eventually even though I'm a degree or two off when I dropped the dist?..
Not too familiar with total timing Bob but always willing to learn something new. My light is adjustable.

1 tooth OFF is close to 12 degrees of timing.

Check the total timing by disconnecting the vacuum advance then checking the timing while revving. At a certain rpm it will quit advancing. Determine what the total timing is by adjusting the timing light dial until the timing mark is zeroed. That will be the total timing. Then trial and error back off the total timing until the knock is reduced. 28 to 34 seems to be the range people use.

That makes sense Dr, considering the size of the balancer and the dist gear. If though, it was off a tooth, wouldn't it run badly, if at all, set at nine degrees at idle? That's not the case here. It's only at 2500 rpm and up that it all goes to hell. I've checked for vacuum leaks possibly making a too lean of a condition. Or is that even relevant? I keep going back to the vac adv since there is only a problem at acceleration when the advance should be kicking in to match the rpm's. Maybe I'll try replacing it.
I'll try that timing method next time I put the light to it Bob. Thanks you guys appreciate the input.

Don't forget the vacuum advance actually retards the timing when u open the throttle

My initial timing, no vacuum at idle is 13 degrees, I can back it down to ZERO and it still idles fine (RPMs a bit lower), take it on the road and it falls on its face. So your nine degrees BTDC, could really be 2-3 degrees ATDC (retarded)

Well Bob, you do lose your manifold vacuum at WOT, but the mechanical advance takes over, there should be no retarding of the timing with increased engine speed, with the exception of "at idle" with the vacuum source attached the carb port.

My point was that at WOT, the vacuum advance isn't adding any more advance

Gotcha

My 400 is a pretty mild build for touring and has always done well at the factory 9B. I'm not understanding why yours is 13 degrees with the adv hose pulled at idle. Do you mean with a tooth off you could be atdc instead of btdc? It actually clears up at wot. It's mainly through the accelerating throttle positions when the vacuum is at it's highest. So doesn't that point to a problem with the advance? There is no changing springs on a vac adv dist is there, just mechanical distributors, correct?

That's my base idle setting. You actually lose vacuum during acceleration until the engine evens out (cruise), that's why you need the mechanical advance as well as vacuum. And yes, depending on which direction you are OFF on the installation, you could be advanced or retarded. You say it runs good at WOT, no pinging? Because in your initial post, you say you are experiencing a lot of pinging/detonation, that equals too advanced.

It starts out nice when I hit second gear is when it pings but it clears up at higher rpm... Time to try re installation That doesn't do it, may have to go back to mech type.

From what you've described it sounds like the timing is ramping up too quickly. If the springs are too light resulting in too much advance for the engine load, it'll ping. However before changing anything, like others have mentioned, check & record the timing profile. I hope they sold you a dist specifically for a Firebird and it isn't configured for a different application?

I have a harmonic balancer with degree marks up to 90 deg. So with my handy old-school timing light I record the timing at every 200 rpm until it stops advancing. I'm currently running a hop-out curve [vs. a linear curve] which a fast and then slow ramp, (per Hot Rod less advance is needed as piston speed increases). If I recall mine is fast from 1000 - 1800 rpm and then slow up to ~3400, with initial at 9-10. I tried to run 12-13 initial and would get what sounded like valve-train noise in 2nd & 3rd gear at cruise. If you run the initial too low, it'll be harder to start and run hotter. I've seen many ponchos with the paint burned off the heads.

Perhaps some of the older readers remember back when you could take a new distributor to your local speed shop and they'd set it up for you. They just needed the weight of the car, and drive-train info. You can't find that service anymore...

Ok, my guess is the vacuum advance is adding too much advance. Try driving it with the vacuum advance disconnected and vacuum line plugged.
Crane makes an adjustable vacuum advance for the HEI.

Vacume advance ADDS timing under high vacuum. Some add too much, or too soon, or both. The Crane adjustable advance has a adjustment to alter this.

It could be as your vacuum comes up it adds advance and thus the pinging. I had to add an adjustable vacuum advance for this very reason. Simple fix.

Oh, and don't worry about the "it's one tooth of stuff." The distributor doesn't care where it sits as long as its housing is rotated to the correct position. A timing light will tell the tale. By this I mean if you put it off 2 teeth (assuming you still line up the oil pump shaft) and then rotate the housing the span of 2 teeth over, it's all the same to the engine. It may be that the vacuum advance causes interference, but the engine runs the same.

Cole , I completely agree with you on the engine not caring about being a tooth off. Like you said, as long as the housing is adjusted for it. Only the vac advance
modulator cares if it runs out of room to adjust. Also if you don't move the engine position while the dis is out, the oil pump shaft will only let you put it on the same tooth it cam out of. (Or 180 degrees off).
Cme469

Do you have the vac advance connected to ported or full vacuum?

These Crane adjustable vacuum advance kits let you tailor your ignition to the advance you want. The adjustability provided by these kits permits you to run the maximum amount of ignition advance throughout the rpm range, without incurring detonation. Once they're installed, you can quickly compensate for changes in fuel quality and altitude. Each kit comes with a vacuum diaphragm, an Allen wrench, advance weight springs, and instructions.