The basics of it are 2 things:

1. disconnect the mixture solenoids on the back off the BBD carb
2. use a Mopar Performance ignition module instead of the factory Dura Spark II and take the computer out of the ignition loop.

This mainly applies to '83 to '86 CJ7's with the computer controlled 258. I don't know whether or not it will work on YJ's with the 258. The article is at http://www.off-road.com/jeep/258ignition.htm

I didn't happen to have a Mopar performance ignition module and wiring harness laying around, so I decided to keep the Dura Spark. The Dura Spark really isn't too bad of an ignition unit and spare parts are easy to find and cheap. Plus I already have a spare pickup coil and ignition module, so I would have really been throwing away twice the parts if I went with the Mopar. If I ever do really upgrade the ignition I'll go with the GM HEI from a Chev straight 6.

I sort of changed the order of the instructions from the write up on the Off-Road.com Jeep tech section to fit my needs (and save some $).

Here's what I did:

1. warmed up the Jeep and got it opperating in closed loop mode (for the last time!)
2. screw in the idle jets so the needles that are connected to the stepper motor move. The purpose of this is to fool the carb into putting the stepper motor driven needles into the full rich position. The needles will be all pushed the way to the inside of the carb and the tone of the air going through the carb will get real low and the engine will slow down and start to miss. When I got to this point I shut off the engine and disconnected the plug for the stepper motors on the back of the carb. The plug stays disconnected from now on.
3. I changed the wiring. This is where my project differs from Off-Road.Com's. They splice in some Mopar parts here, but I kept what I had and bypassed the computer. On '83 and later CJ's with the 4.2 the purple and orange wires from the distributor go to the computer under the dash instead of directly to the ignition module like earlier CJ's with Dura Spark. The summary is: Orange wire at distributor connects to orange wire at ignition module, Purple wire from distributor connects to purple wire at ignition module. Pull the wires out of the split loom covering and follow them carefully. Both orange and purple wire from the distributor go into the firewall between the battery and valve cover, there is also an orange wire from the igntion module that goes into the firewall at the same place. Cut the two orange wires and splice them together, also cut the purple wire here. There is no purple wire coming out from the plug near the ignition module, so you will have to splice into the purple wire between the ingnition module and the plug and run the wire up to where you cut the other purple wire. I used 16 Ga wire for the section I added and I used insulated spade terminals at all the connections. A perfectionist would have soldered and used heat shrink tubing to insulate the connections.
4. As suggested in the article on Off-Road.com I teed the vaccum line on the distributor into the ported vaccum. This vaccum comes out of the BBD on the side towards the valve cover, about 1/2 way up the carb.
5. I set my timing. I disconnected the vaccum line at the distributor and plugged it, and set the timing to 8 degrees BTDC. When I first fired it up the timing was way retarded (maybe 6 degrees ATDC) and the engine was heating up fast from the timing being so retarded, so don't let it idle long before you re-set your timing. After I set it right it ran great. The idle was way smoother than it had been in a long time.

The Results: My 258 now revs smoothly to 4000 RPM. Thats right 4000 RPM. Before this it would only get to 3000 RPM and then start to bog and miss. It also has a bit more power below 3000 RPM and the low end torque is defintiley stronger at 600 RPM than it used to be. I idled up a fairly steep driveway in 1st gear high range and it went down to 400 RPM and kept
pulling, before the conversion the engine always died when I did this in this driveway.

John Nutter
85 CJ7