Need opinions on timing bounce over 5K

[techweenie]

I have an otherwise good-running, recently rebuilt CIS 2.7 that is now on its third distributor (with optical breaker). The prior distibutors didn't seem to be able to advance all the way, for some reason. The engine runs very strong to 5K and then cr@ps out.

The timing light shows that over 5K, timing bounces 5-8 degrees (!)

One possible cause would be the distributor drive gear on the crank, but why would that only affect 5K plus? The distributor shaft doesn't seem loose...

Is there an intermediate step before going to a crankfire solution?

Is there something I'm overlooking?

TIA

[Early_S_Man]

In my experience ... large timing variations in the vacuum-equipped 2.4 - 3.0 distributors are caused by:

1. worn out distributor bushings, or

2. missing shims or fiber spacer washers on the distributor shaft above the gear.

3. sticking centrifugal advance mechanism

4. loose point plate

Disassembly, cleaning, and inspection of one or more of your distributors would seem to be called for ...

distributor lube...

[techweenie]

Excellent! Thank you!