1920 Carb

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oneway71

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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)

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. Runs great if you go easy on the gas. I need to feather the gas to keep running to rev up faster without stall.

Question.... Do these have an accelerator pump? If so where? I have looked at diagrams and not found one.

How does it get that extra squirt of gas when needed?

I wonder what vacuum lines can be removed? It has the delayed advance to the distributor and I would like to eliminate that.

All my other slants have 2 barrels and I know those carbs....not this one.

I could swap out my intake and go with a 2 but this car is very nice and I want to keep it close to original!

Thanks
 
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)

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. Runs great if you go easy on the gas. I need to feather the gas to keep running to rev up faster without stall.

Question.... Do these have an accelerator pump? If so where? I have looked at diagrams and not found one.

How does it get that extra squirt of gas when needed?

I wonder what vacuum lines can be removed? It has the delayed advance to the distributor and I would like to eliminate that.

All my other slants have 2 barrels and I know those carbs....not this one.

I could swap out my intake and go with a 2 but this car is very nice and I want to keep it close to original!

Thanks
Click to expand...

I'm going off of memory but there aren't many lines that should go to the carb. You should have the hose going from the distributor to the carb with no widgets in between. If the hose connects to something else before the carb, then disconnect it and run that line straight.

What other vacuum lines are connected to it?

The accel pump should be in the float bowl. Take the cover off and you'll see it right there. Before you do that, take a look down the carb and pull down the accelerator linkage and make sure you get a strong shot of fuel as soon as you pull the linkage. Do that with the car off of course :D. That'll tell you if its the accel pump or not.

Make sure you have no vacuum leaks and have it timed around 8* BTDC. Having the timing too retarded can cause a slight hesitation as well.
 
Thanks for the advice.

I do get a good strong squirt; maybe I have something else going on with it.

I have no vacuum leaks and I do have the vacuum routing diagram. I will probably eliminate the EGR and large circle canister (OSAR....iirc, probably not correct label) mounted near the intake, lines that go to the radiator also.

I will play more before I buy a carb or switch out to 2 brrl
 
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)
Click to expand...

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.
Click to expand...

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?
Click to expand...

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?
Click to expand...

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.
 
ESP47 said:
I'm going off of memory but there aren't many lines that should go to the carb.
Click to expand...

1. from carb throttle body to PCV valve
2. from carb bowl vent to charcoal can (vent)
3. from charcoal can to carb throttle body (purge)
4. from carb venturi to EGR vacuum amplifier
5. from carb throttle body to thermostatic air cleaner
6. from carb throttle body to choke pull-off

The accel pump should be in the float bowl. Take the cover off and you'll see it right there.
Click to expand...

Nope. You can't see the accelerator pump until you remove the main metering block.
 
SSD Thanks. I read all the threads I could find on this before I posted but was still a little confused.

Vacuum amplifier is still hooked up but the PO unhooked the OSAC valve. And one line from the VAC Amp is plugged.

I will clean things up, check the accel pump, check again for vacuum leaks and go from there.

Thanks again!

Has anyone found a rebuild kit for these carbs for under $50? I am shocked at how much the kits have gone up. Last one I bought was less than $20.
 
Rebuild kit quality and completeness has been dropping rapidly over the last few years. Don't overpay for a simple gasket kit, but do buy a quality kit. I like the ones from www.daytonaparts.com (redesigned inlet needle and seat works better).
 
After driving the car more, and paying closer attention, I have come to the conclusion that the problem is boiling fuel and not the carb. I can watch the bubbles and it happens when I stop at lights. If I am on a hill it seems even worse. I also have a problem starting the car after sitting for a few minutes.

So a fuel line mod is in order.
 
I eliminated all the extra CARB (california air resource board) parts on my car including the vacuum amp, EGR valve, and extra vacuum lines.

The car now runs great! It is smoother and drives easier; although I still have an issue starting while it is warm because of gas boil. I will do the fuel line mod next.
 
I got a 1920 rebuild kit for under 15 bucks at Autozone not a month ago, came with both type accelerator pumps. They even stocked it. If it wasnt autozone, it was Oreilly, but it WAS one of these. I stated 64 Dart and they handed me the kit! When the Accelerator pump fails it will start spewing gas out of a tiny hole on the carb body on the back of the cast bowl whenever you goose it.
 
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