1978 Chrysler LeBaron~ Stuck and I need help!!!
I am working on a 1978 Lebaron with a 318 rebuilt to factory specs, the only modification that has been made is the addition of a 4 barrel carbeurator in place of the 2 barrel. Now, we can get her to run strong on the warm up and the idle, but while test driving there seems to be way too much gas and not enough spark. Adjustment of the distributer as well as carbeurator seem futile. Also, there is an electric ignition module that was sciliconed to the firewall that has since melted off. This distributor is foriegn to me as it is electronically controlled and not controlled by vacuum lines. We can afford to fix the electric module (new ones are not attainable) or get a vacuum controlled distributor but not both.
NEED this question answered first: Should the spark conrol computer be compatible with an aftermarket 4 barrel carb?
Then this question: If the spark control computer will not be compatible with the 4 barrel can I replace the distributor with a vacuum control distributor and have no computer?
NEED this question answered first: Should the spark conrol computer be compatible with an aftermarket 4 barrel carb?
Then this question: If the spark control computer will not be compatible with the 4 barrel can I replace the distributor with a vacuum control distributor and have no computer?
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Comments
The vehicle you are working on was originally built as a "lean burn" model; which (unless my memory fails me) has the ignition module built into the spark control computer on the air cleaner. Again; if I remember correctly; the module on the firewall is not an ignition module. It is an ambient air temperature sensor; which controls the fuel enrichment, and/or the EGR system activation. You might be able to find a used or an unsold new one from an Internet source. Depending on the parts that are damaged, it may not be repairable. Somebody may have mounted an ignition module from a non-lean burn Chrysler on the firewall, and attempted to use it to bypass the module in the spark control computer; but I don't believe there was one there originally on the lean burn model.
There is a vacuum diaphragm on the spark control computer; which for all practical purposes is equivalent to the vacuum advance diaphragm on a distributor. However; I do not recall whether this diaphragm is intended to be driven by ported vacuum or full manifold vacuum. A little experimentation should sort that out. But hooking up that diaphragm to a suitable vacuum source might make a great big difference in the running quality.
The potential compatibility of the 4 barrel carb you have will partly depend on the brand and type of intake manifold you are using; as well as the brand, CFM rating, and model of aftermarket carb. Please post that information in your response.
Some of the richness you are experiencing may come from a choke pull off diaphragm (also called a choke vacuum break) which is not connected to a vacuum hose, or is not adjusted properly; or has a ruptured diaphragm.
The 1978 Le Baron 318 was available with a choice of 2 barrel or 4 barrel carb. The stock replacement Carter Thermo Quad 4 barrel is available rebuilt from rock auto for about $262 plus shipping. I'll say more about carbs after hearing from you in answer to the questions I raised.
The problem here is that your car was manufactured with a low compression ratio, along with air injection, plus lots of exhaust gas recirculation and a severely restricted exhaust system, and in addition has stock timing sprockets that are machined with retarded keyways (which was a 1970's Chrysler trick to reduce emissions at the expense of performance). ALL of these things should be changed; if you hope to make it run any better than a stock motor.
The most important changes are to disconnect the air injection pump, but leave the check valve at the exhaust manifolds in place. If the intake manifold has an EGR valve; disconnect and plug the vacuum hose to that valve.
The stock catalytic converter has surely become very clogged in 33 years of use; and if it is still there; is now killing your power and messing up the fuel mixture. I would strongly recommend either replacing the catalytic converter with a straight pipe; or installing a high flow converter in its place. You can keep a single exhaust system; but I would recommend using a low restriction muffler. I'll give you a muffler recommendation, if you tell me your preference of quiet, mellow, or radical sounding.
Buy a Clevite/Perfect Circle # 93103 timing set with 3 keyways and a heavy duty double row roller chain ($56.79 from Rock Auto). Set the cam timing to one of the more advanced settings. It will take some experimentation to find the best keyway to use; but it definitely will not be on the retarded side.
The carb cannot be adjusted for performance by just turning the idle mixture screws; that does not affect the mixture in the speed and load ranges you need. For real performance improvement; it will require changing the metering rods and jets. Edelbrock makes a calibration kit for the 600cfm performer; which has a full assortment of metering needles, springs, and main jets. If you don't have one; buy it. You'll need to know the carb number to get the right kit. (http://www.summitracing.com/search/Brand/Edelbrock/Carburetor-Model/Performer/P- art-Type/Carburetor-Calibration-Kits/?Ns=Rank|Asc) That will be one of the most effective things you can do; but all the other things I mentioned above will each change the fuel mixture; so there is little point in trying to tune the carb until after you get all the mechanical settings right.
If anyone can help I'd be glad to give them use of my 45 years in the horse business!