On another note with 10.7:1 compression and iron heads you really cant put too much timing in. That cc503 will build lots of cylinder pressure down low. You could be seeing detonation under load. Vortecs in general dont like much more then 32* total at full advance. You running a Knock sensor?

Need a little more info on the ignition system.

BTW your slack looks normal

 

With the vacuum advance unplugged on the distributor, I've set base ignition timing to 13 degrees, the only advance in use is the mechanical weights & springs. While watching the harmonic balancer with a timing light, when I give the engine any throttle I can watch the timing mark retard by more than 20 degrees before it will advance like normal.

At idle the timing isn't speratic, it's a consistent 13 degrees without any hunting or timing mark movement. When the timing does pull it's a fast and fluent retarding immediately when I move the throttle on the carb. The timing will stay consistently retard for a couple seconds before advancing. When it does advance, it too isn't speratic and will allow me to set my max timing at 36 degrees all in by 3000rpm. When the engine returns to idle it's dead on at 13 degrees.

These are patriot heads with a vortec intake bolt pattern, not true vortecs. Any more than 36-38 degrees of timing I do begin to run into pinging. Any less timing and the engine isn't nearly as peppy.

The ignition is:
Summit 850055 distributor with a VC1810 vac advance can, on ported vac.
MSD 6a
Accel coil
Taylor wires
NGK TR6 gaped @ .055"

 

Time to play with the mechanical advance use a heavier weight with the same spiring. Or a lighter spring with the same weight, whatever you can get your hands on

 

Really, you think the problem is the mechanical advance not coming in soon enough? How would that cause such a drastic timing retard below initial timing?

 

There's really nothing else that will effect your timing. Your set-up is very simple not much to go wrong. also check it with the vacuum hooked up

 

I am kinda rough on SBC tech, but is your engine making enough vacuum off idle to operate the vacuum adv distributor? It seems like, from what you have already said, that everything is operating normally, except in that transitional period from idle to acceleration.

 

I recently did a GenI top end. I installed a new comp cam and edelbrock intake and carb. I was going to use a button, but comp told me it wasn't needed. I think if has a bearing that prevents wear on the back face of the timing cover. Do those thrust washers go behind the cam chain wheel? If so how are they secured?

 

Where's the smiley with the bucket of popcorn? The one that says "I'm really curious to see how this turns out". All we have is a half-dozen flipping you off or mooning you or something. We even have a bat-angel...?

Anyways, I'd really like to know what could cause the ignition to retard 20 degrees, but spot-on at idle and full advance... :pop:

 

You and me both man

 

Any progress Mykk ?