Thanks to this forum's search function which allowed us to diagnose the following.
Recently purchased 74-911 (stock with CIS) was backfiring thru exhaust pretty bad upon decel. Checked the timing with vacuum connected at 900 RPM and was at 0 degrees. It is suppose to be 5 ADTC. Reset timing and car was even worse. Then checked at 6000 RPM with vacuum disconnected (all per manual) and found there was no mechanical advance upon reving motor.
Pulled dizzy, (stock Bosch 0 231 169 008) disassembled and found the mechanical advance was frozen solid. See photo. By applying penetrating oil and WD-40 finally got the mechanism to work properly. But we cannot figure how to get the rotor (top) portion of the mechanism off so we could clean up the shaft. The felt plug in center of the top of shaft was removed but there is not set screw or clip, so we are at a loss of how to remove.
By continually flushing the parts with penetrating oil, the mechanism is now free. Dizzy reinstalled, timing set per factory and car runs great-no more backfire. But would like to thoroughly clean the parts so how does the top portion get removed?
Thanks again
Jeff
-74 911
PS, during reviewing prior posts, there was some discussion where the vacuum advance was totally disconnect to allow car to run even better. If this is true what are the gains by doing so? So what would the timing be set at at 900 RPM with vacuum disconnected or does one and just set the timing at the 30-35 degrees BTDC at 6000 RPM and be done with it?
