Thanks David,
That's my plan. But, that does not fully explain why after the numerous test drives, that the timing is at 28 deg. BTDC (with the vac. line connected) and upon removing the vac. line that the timing only drops to 24 deg. BTDC. It's almost as if the distributor has moved during the test drives, but I've marked it and can confirm that it has not. Only other reason I can think of is a sticking advance unit on the new distributor.

I plan to reroute the vac. line to provide Ported source only (bypass that valve), test drive and recheck timing. If it is still misbehaving, I will start by contacting Summit as they supplied the Distributor.

 

Morning David (and all),
Results of yesterdays tests with a vacuum gauge are attached. The chart details the exact sequence of checks accomplished and their effects on the engine.

To clarify a few questions that may arise:
1) The distributor is not moving around on its clamp.
2) The damper is not separated and slipping.

My conclusion is that something is sticking within the distributor. Either the mechanical or Vacuum advance. I will be contacting Summit as they supplied it. In the interim, I will reinstall the original unit and coil.

 

Morning David (and all),
Results of yesterdays tests with a vacuum gauge are attached. The chart details the exact sequence of checks accomplished and their effects on the engine.

To clarify a few questions that may arise:
1) The distributor is not moving around on its clamp.
2) The damper is not separated and slipping.

My conclusion is that something is sticking within the distributor. Either the mechanical or Vacuum advance. I will be contacting Summit as they supplied it. In the interim, I will reinstall the original unit and coil.

 

David,
Summit replied as follows.

"Hello Sir, I apologize for the inconvenience. Yes you can open up this distributor and check for advance binding. Please do so to see if this fixes your problem. Let me know if you have any other questions."

So I opened it up. The advance rod from the vac. capsule does not align properly with the pin on the advance plate. Where it enters the distributor body it rubs against the rough cast slot in the dist. body, pushing the rod upwards so it cannot slide around easily on the pin. See attached diagram.

The mechanical advance seemed fine, but I would have expected evidence of a bit of factory lube on the weights and pivots. But, everything seemed to move easily and the springs did retract the weights.

I filed the Distributor body to give the rod some clearance and put a slight bend in the rod so it engages easily with the pin.

So this is what I presume was happening. Initial installation all good. When the engine is revved the higher ported vacuum advances the unit and it operates as it should. Upon returning to idle rpm, the advance rod does not retract resulting in a highly advanced timing condition. Shutting down the engine kills the vacuum supply, but the distributor remains in an advanced state resulting in hard starting and very rough idle. Additionally, checking the vacuum readings by "teeing" off the dist. supply line leads one to almost believe that the actual distributor has moved, as there is no irregularity in the supply itself. But of course it has not. Leave it alone overnight or bang around the distributor eventually allows the rod to slip back to its correct position and the car will start and idle normally again until it is revved up and the rod sticks again.

I will be installing it within a few days and will advise on how this works out.