I'm thinking about making a sleeper out of my 78 lebaron. should I keep the lean burn, or ditch it. how tunable is it

DITCH IT.

It is not real tunable. It had some reliability issues....okay, a lot of reliability issues. The concept of having electronics on top of an engine in all the heat does not make for a real reliable set up. It was, IMHO, a decent idea but poorly executed.
Most have yanked the lean burn and gone to a regular vacuum/mechanical advance system that does tune a lot easier.
Craig

Mopar Action article "trash that lean burn". Did that to an 86 Chrysler, simple and effective.

Do not even think about keeping it.... Very simple to convert to a regular electronic ignition and regular carb of various sorts.

Toss it. Replace with a standard carb and electronic ignition. World of difference. Wiring will be a little work, a service manual for your car and a non lean burn wiring diagram will help immensely.

78 should already have a ballast resistor for that generation computer so some of the wiring is already done for you. You just need to do the rest of it and the the distributor and different carberator.

Perhaps one of Chrysler's worst nightmares, trash it...I've converted a few, install a factory or aftermarket manifold/carb system of your choice, use a Chrysler single point vac adv. dist. install a Pertronix conversion kit along with the proper coil, do have a factory service manual so you can you can eliminate the computer, half the harness nightmare, along with the ballast resistor(s)correctly for a trouble free system that's reliable

Had a 5th Ave lone time ago. Typical totally underpowered 318. One time it failed to start, no spark.

In order to get it home I brought a spare points distributor and a jumper wire. Not only was I happy that we did not have to hire a tow truck but this 5th that would previously barely climb a speed bump was now spinning the rear tire. So it could now lay rubber and it felt like it picked up 50hp.

We then converted to the MP elec ign w the orange box. To this day it makes me wonder why anyone would put up with the lack of power the Lean Burn cars had.

back when lean burn was new, i owned a junk yard [which was the correct term for a place that bought and sold junk cars. i know, the term is hard to believe !]. we sold all the points and electronic distributors plus wiring and matching coils and carbs we could come up with. this was to individuals, repair shops, and dealers alike. nobody could get those systems to run correctly. made a pretty good buck on just those conversions when those conversions were not really a "kit" item.