Odd fire refers to a special Buick engine that was manufactured in the 60 and 70's. Essently the GM engineering team removed 2 cylinders from a v8 engine making it a v6. The result was a distributor that looked like it should be mounted on a v8 however it was missing 2 spark plug connectors and the triggering rotor in the distributor that was missing 2 teeth. Another significant differance was the engine didn't have stepped crankshaft. Cylinders 1 and 3, 2 and 4, 3 and 6, shared the same crankshaft journals. The way the engine ran was 123_567_ the spaces being pauses where the 4th and 8th cylinders should have been. The result was a engine that has a little better milage. The Jeep heads love this engine since it has a significant amount of torque. The reason being is when GM manufactured the engine they had to increase the mass of the flywheel beyond what was normally used for a similar sized engine. The larger flywheel would absorb the oddfiring balance problems with the engine and give the impression the engine had a lot of torque. After a few years GM installed a stepped crank and made the engine an even firing unit. A lot of shade tree mechanics really screwed up these engines by installing an even firing distributor on the engine. The engine would run poorley and backfire quite a bit. Essently the ignition timing would only be correct for the 1st and 3rd cylinder the other 4 cylinders would be severly advanced or retarded. The result was usually burned pistons from preignition if the engine was operated for an extended time.
The little ford duraspark distributor you have taken a photo of came from an even firing engine. The engine that distributor came out of was a straight six or a V 6 with a stepped crank. The European v6 installed in Rangers was an even firing unit with a stepped crank.
