1920 Carb

oneway71 said
I have a '73 Duster with 39k on it. It has 225 with a Holley 1920 1 brrl. It appears to have CARB emissions. (California car)

The first thing you're going to want to do is connect the distributor vacuum advance directly to the carburetor's spark advance port, bypassing the OSAC valve mounted on the passenger side of the firewall. This will greatly reduce the hesitation and improve driveability, performance, and fuel economy with no downsides.

It has a dead spot under quick acceleration. Sometimes it will stall out, sometimes I can keep it running. It acts as if it is not getting enough gas then.

Faulty accelerator pump (and you'll also want to check to make sure the vacuum advance pod on the distributor hasn't got a blown diaphragm or a cracked or holed hose).

Question.... Do these have an accelerator pump? If so where?

Yep, it's a rubber diaphragm sandwiched between the main metering block and the main body, driven by a compression spring and pull-rod, which in turn is pulled by a nylon pivot cam connected by a small "S"-shaped link to the throttle lever. The pull-rod, the pivot cam, and the link are all easily visible on the passenger side of the carburetor. Carburetor operation and repair manuals and links to training movies and carb repair/modification threads are posted here for free download.

I wonder what vacuum lines can be removed?

In addition to bypassing the OSAC, you may want to eliminate the EGR. This can be done by simply putting an appropriately-sized ball bearing in the vacuum hose connected to the EGR valve itself, or if you'd like to clean up the engine bay, you can remove the vacuum amplifier (the hockey puck lookin' thing mounted to the cylinder head between the air cleaner and the valve cover) and all hoses connected to it -- one runs to manifold vacuum tap on rearmost intake runner, one runs to coolant temp sensor in top tank of radiator, and from there to EGR valve, and one runs to venturi vacuum nipple on the carburetor. The intake vacuum tap and the carburetor venturi vacuum tap must be securely capped to make sure no vacuum leaks.

Once you've done this, next you can turn your attention to the basic ignition timing. Spec of 0° (TDC) on the '73s makes for sluggish acceleration, but you can't advance too far without upsetting idle speed and getting spark knock. Try 2.5° BTDC (with vacuum advance disconnected and engine idle speed set to 700 rpm) and see how she goes. If no ping and no difficulty maintaining idle speed, try 5°.

While you are working on that '73, tune-up parts and technique suggestions in this thread. You'll also want to do the Fuel line mod.