Bang for the buck, the Duraspark II distributor is hard to beat as a triggering devise for an electronic ignition system. Coupled with either the sock ignition box or an aftermarket control box (such as as the Dyna Module or MSD-6A) it is a tough, readily available, reliable distributor.

Ford began using electronic ignitions in 1973 and introduced the Duraspark II system in 1976. The biggest change, apart from the control box redesign, was the large distributor cap to handle the increased spark energy. The system consists of a magnetic reluctor and pickup in the distributor, and an ignition module to trigger the coil. Typically, the distributors have both mechanical and vacuum advance mechanisms. The curve is reset by using inexpensive springs and adjustable advance units. They are found on both 200 and 250 engines and are interchangeable. 

They are a direct fit on older 200/250 engines built after 1964 with the 5/16" oil pump drive shaft. If you want to get one from the auto parts store, make it easy on the clerk and just ask for a distributor from a '78 or '79 Fairmont. Classic Inlines also offers a performance DSII Distributor and complete kits, which utilize a full length bronze oil impregnated bushing to provide increased durability and cure top end timing fluctuations which are common in OEM DSII distributors.

The Duraspark distributor can be wired to various ignition control modules.

1. GM 4-pin module - This makes for a very clean and easy setup. Any of the early mid seventies to early eighties GM cars have this module.
   
2. Ford Blue Strain Module - When selecting the module, the one to ask for is the one with a "blue strain relief" or the "49 state" module (shown above).
3. Dyna module - with the matching Inferno coil (sold by Classic Inlines) is an excellent choice and easy to wire (shown below).
4. MSD 6A module - or other after market ignition systems. The MSD can be used as a stand-alone or in conjunction with the stock Ford module.

Dyna Module and Inferno Coil by Performance Distributors click here for more information

Spark plug gaps may be set much wider with the Duraspark. Using the stock module, set plug gaps between .045" - .060". With an after market module, check the manufacturers recommendation. My 67 coupe uses the MSD6A as a stand-alone with plug gaps of .050", my 66 coupe uses the Dyna Module and Inferno Coil with plug gaps of .055".

The module needs to be mounted on an aluminum or steel backing to dissipate heat, which also grounds the module. The ignition wiring diagram looks daunting but its not really that difficult. Most installs only need two connections. The red wire which is connected to a switched 12V source and the white wire which goes to the start terminal of the ignition switch. The white wire is optional. When used it retards the spark a couple of degrees to reduce the load on the starter (an enterprising hot rodder might hook this up to a nitrous switch to retard the spark when the juice is on). The Dyna and MSD modules come with wiring instructions, were not sure about the GM or Ford module, but would guess they do. If not, they can be found online, as many websites document the installation.

If you have a DuraSpark II distributor, you also have smog-control spark advance curves inside. All of the DuraSpark units came this way, to reduce hydrocarbons. Unfortunately, it also reduces MPG. However... today's gasoline reduces the hydrocarbons for you, even more than the slow spark curve did. So, get a set of the Mr. Gasket #925D distributor springs and modify your distributor as follows: First, remove the lighter of the 2 springs in the DII and replace it with one of the #925D springs. DO NOT replace both springs with the #925D springs (more on that in a moment). Next, there is a support arm that holds the larger spring, on it's non-slotted end. Bend this arm in toward the center of the distributor, just 3/32 of an inch.

This combination replicates the "police interceptor" distributor spark curve for the 200 I-6, according to a local "guru" who helped build these for Ford in the early 1980s. It causes earlier spark advance up to 1200 RPM, which then remains steady until 1800 RPM, when the secondary spring starts its advance. This "plateau" of early advance, limited by the 3/32" inward adjustment of the heavier spring, provides more torque at around-town speeds. This improves your MPG because you don't have to open the throttle as far to get the same speeds you were running before. You'll also notice better off-the-line pep and cold-running performance. Mine also starts a little better when hot, and the plugs stay cleaner. My in-town MPG rose from 16.5 average to 18.1 average over 2 tanks of gas, winter driving to and from work. I haven't tested the highway MPG yet, but I don't think it will improve from the 23+ I've been getting. I'll re-post if it does.

If you make the mistake of replacing BOTH springs in your DII with the #925D springs, you will get a SLOWER spark curve unless you extensively modify one of them to provide a "slot", like the heavier spring already has. But I found, even after that exercise, that the engine "hit the wall" at about 2200 RPM and would not accelerate well up hills. Adding in the heavier spring, but delaying its effect until 2000 RPM, did the trick: now it loves to rev, even on regular gas (my compression is about 9.4:1). The maximum advance is reached at 2600 RPM on my engine with this mod: before, the max advance was at 3200 RPM.