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What sacrifice needed to get Holley 1920 to idle?
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Author:  Joshie225 [ Fri Aug 31, 2007 9:13 pm ]
Post subject:  What sacrifice needed to get Holley 1920 to idle?
The good news is after all my recent and past efforts my '67 V100 now runs and drives. The bad news is it won't idle and stalls. The idle mixture screw makes little difference if any. I went through the carb last October, but it wouldn't idle then either and I never drove the car. I recently found the gas tank full of rust and garbage. Even though I put in a new fuel filter I suspect the carb might have ingested some junk and suffered internal blockage.

Most of my bygone Holley 1920s had dead accelerator pumps. This 1920 has a good pump shot, but won't idle. The car goes down the road fine and has pretty good power, but the stalling stinks.

I know I'm tearing back into the carb tomorrow. Any advice on what to look for when I've got it apart? I could also use a carb kit recommendation as the float bowl gasket from my last kit swelled up enough that it wouldn't fit without puckering. I had some gasket material and made a fiber gasket, but it's weeping.
Author:  Dart270 [ Sat Sep 01, 2007 7:52 am ]
Post subject: 
You've likely done this, but my standard response to this question is: "Have you adjusted the valves recently/ever?"

Tight valves will give you those symptoms.

Sprayed some carb cleaner arond the base while running - vac leaks?

There should be nothing inherent about the 1920 that idles poorly, unless is trashed inside, as you suspect.

Float level would be another check. I don't remember ever having a 1920 give me a poor idle - always something else.

Lou
Author:  Doctor Dodge [ Sat Sep 01, 2007 8:55 am ]
Post subject: 
Do check all the other systems as suggested. Make sure it is a carb problem before proceeding.

Here is a basic Holley idle circuit:
Image

On a used 1920 with the history you discribed, the idle feed restriction or idle circuit inlet point is usually plugged with junk. The trouble is that this is inside the 1920's metering block and can not be easily accessed. Plan A is to trace the idle circuit pathway and "back-flush" this passages with carb cleaner and compresses air.

Other trouble areas are related to the vacuum needed to draw the fuel thru the idle circuit. If the throttle blade is too far open or if there is "damage" (modification) at the transfer slot, idle fuel flow will change or stop completly. There is some correction for this up at the idle air bleed, this is the larger of the two presses-in brass openings you see when looking down into the venturi, reducing the air bleed increases the idle fuel flow.
I often use a long pencle with a rubber eraser to reach into and plug - partially plug this bleed while the engine is running. This changes the idle condition and allows you to see if adjusting the air bleed size will help the idle quality.
DD
Author:  SlantSixDan [ Sat Sep 01, 2007 12:33 pm ]
Post subject: 
Doug's pointed you in the right directions. His caution about the metering block sometimes being irretrievably clogged is also a valid one.

Sometimes I find I can get recalcitrant 1920s to start idling again by using a good brand of spray carburetor cleaner (I like Berryman B12). Focus on the two holes facing skyward in the venturi. I put the spray straw firmly against the pinhole and give a good long blast. Then I move the spray straw to the larger hole and give a similar long blast. Then I start the engine (which will probably be somewhat flooded), hold it at a very fast idle and repeat the two blasts several times.
Author:  Joshie225 [ Sat Sep 01, 2007 8:52 pm ]
Post subject:  Success!
Thanks to Doug and Dan I have an idle. It's a lumpy idle, but at least it stays running. Most of my slants with bad 1920s in the past got a Carter BBS so they would run right. I'm glad I didn't have to resort to that this time.

I tore into the carb and found the passages in the carb body were clear so that left the idle restriction in the metering block. I figured out which hole in the metering block feeds the idle circuit, blocked off the main circuit feed hole with my thumb and pressurized the main well with a rubber tipped blow gun. I put soapy water in the idle feed passage and got it to blow bubbles. I then soaked the main body for about 25 minutes in my can of carburetor cleaner just to be safe. I repeated the soapy water and blow gun routine and again got bubbles. I reassembled the carb and got the engine to idle. Now the idle mixture screw actually does something!

Thanks again to Doug for the tip on idle air bleed. Covering it with an eraser certainly changed the idle. The speed dropped and it smoothed out. I'm thinking if the valve adjustment and general tune-up doesn't get me a good idle I'll play with the idle air bleed.

Tune-up will wait until tomorrow or Monday. Maybe replacing the plug wires that are date coded 1-67 will help? ;-)
Author:  Doctor Dodge [ Sun Sep 02, 2007 9:28 pm ]
Post subject: 
Quote:
...Thanks again for the tip on idle air bleed. Covering it with an eraser certainly changed the idle. The speed dropped and it smoothed out...
I have improved the idle quality on a few 1920 by changing the idle air bleed size.
I have some old 'rosin core" solder that happens to be the right size to drive into the air bleed hole. I clean-out the core material then peen a small piece of the "hollow solder into the air bleed. I use small drills mounted in a "pin vise" to size the new hole for the best idle.
DD
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