Carb Problems: Holley 1920:
OSAC valve? No clue. Sounds like something to throw away
The OSAC (Orifice Spark Advance Control) valve is indeed something to bypass. Its function is to delay the vacuum signal to the distributor vacuum advance by 7, 17, or 27 seconds (depending on the particular valve, which in turn depended on the particular model/engine/transmission/emissions package). This was to reduce NOx emissions to squeak the cars past the new-at-the-time Federal emissions certification tests, of which passage was mandatory if the automaker wanted to sell the cars when they were new. The OSAC system is notorious for causing rotten driveability. Hesitation, poor accceleration, and poor part-throttle fuel economy. Run the vacuum hose directly from the carburetor to the distributor vacuum advance.
But all of that is academic, because the OSAC valve, like the EGR valve, did not appear until 1973; this car doesn't have one. The engine in this
1972 car, or at least the intake & exhaust manifolds and carburetor, are from a '73 or later vehicle. That's why there's been so much hacking and plugging and rerouting.
The carbon canister holds fuel vapors until a high vacuum situation arises (you chop the throttle) and the vapors are sucked into the intake instead of polluting the air.
Almost. The charcoal can holds fuel vapours vented from the fuel tank and carburetor bowl not until you chop the throttle, but until you raise the throttle opening a certain amount above idle, at which point vacuum is routed to the can purge port, drawing air through the can to purge the fuel vapours and burn them.
The charcoal can is at the right front corner of the engine compartment, and hooking it up correctly isn't difficult. See
here.
Photo 1 item 1 is the vacuum port for the exhaust gas recirculation valve (EGR).
No, it's the vacuum port for the thermostatic air cleaner. There is no vacuum port on the carburetor that should be connected to the EGR valve itself. The only EGR-related vacuum port on the 1920 is on the other side of the carb, hidden in photo #2 by the bowl vent tube, and it would be connected to the EGR vacuum amplifier, which looks like a hockey puck and — on EGR-equipped cars — is mounted to one of the cylinder head's lifting bosses, roughly top-centre on the manifold side. This 1972 car would not have (does not have, by the photos) an EGR vacuum amplifier or any of the rest of the EGR control system, so nothing should be connected to the EGR valve, which will just sit there on the intake manifold not hurting anything.
Photo 1 item 3 looks to me like you should move the throttle cable to the link currently occupied by the kickdown linkage.
Correct, these two are swapped. And yes, there's a spring missing: The kickdown rod return spring. You can still order one from your local dealer or
www.chryslerpartsdirect.com under part number 4027 590. The top hooks into the small hole in the clip that retains the kickdown pushrod to the carburetor's throttle lever; the bottom hooks to the stud on the pivot that fits through the slotted end of the kickdown pushrod.
Photo 2 item 1 should have a tab under the choke pull off cover bolt for the return spring. If what you have is working, don't get in a lather about it.
Disagree. The throttle return spring bracket is safer than the setup pictured, which will eventually cause the throttle return spring to break due to bending stress. Multiple problems can be solved at once by installing one of the
Electric choke kits. Not only are they adjustable (the '73-up factory "electric assist" chokes are not adjustable), but the kit #1234, applicable for this vehicle, includes a nice throttle spring return bracket built into the new choke's mounting base.
Photo 2 item 2 is the ported vacuum for the distributor advance. You need to run a line from there to the vacuum advance on the distributor. Lose the vacuum advance line you now have and plug the source.
Agreed.
The biggest problem I see in these photos is the wire running to the choke pull off is not connected. This wire needs a 12v source to open the choke, preferably one that has 12v when the ignition is on.
There is never a wire to the choke pull-off, which is the vacuum diaphragm mounted at the top rear of the carburetor. The wire to the choke
thermostat, in this factory electric-assist setup, needs to come from the choke thermostat modulator (which, again, this '72 car does not have — another good reason to install the electric choke kit!). Running it to key-on 12v will cause the choke to come off too quickly and cause cold-engine driveability problems.
The biggest problem I see is the dangerous location of the fuel filter directly over the very hot exhaust manifold. Either put it back where the factory put it or — better — do the
fuel line mod.
BTW, if you're trying to identify this carb, the type number you need is stamped into the front-facing surface at the top of the carb. It'll start with an R, and may be preceeded by the word "LIST", as in "LIST R6756".
