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| carb "idle" issue. https://slantsix.org/forum/viewtopic.php?t=58527 |
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| Author: | ddonner [ Mon Oct 12, 2015 9:54 am ] |
| Post subject: | carb "idle" issue. |
Ok, I have a puzzlement. Holley 1920 carb. For years the Cuda has ran acceptable. Then I went through a "pulling a too heavy trailer" experience and knocked some debris loose from the fuel tank. I replaced filter and life was good. A week or two later, the Cuda developed a "die upon braking" issue. The idle would be fine (auto: 800 - 1000) at rest or while coasting, then drop to below 500 and the engine would die upon braking. Non-power brakes, in case you were wondering. Also I was unable to discover a vacuum leak. a couple weeks later the Cuda developed a "stalling while driving above 40 mph" issue. I nursed her home by pumping the gas. I took apart the Holley 1920, discovered considerable debris in the carb's gas bowl, cleaned carb (internals and bowl), gas lines, blew back into tank, replaced fuel pump and filters. She started and idled good. She ran good -- except for that pesky "die upon braking issue". Again, non-power brakes and I have been unable to discover a vacuum leak. I suspect some debris in some critical part of the carb that blocks gas from passing when the front end "dips". But I'm not a carb guy. Anyone have any thoughts/suggestions? Thanks. Don |
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| Author: | Jsp [ Mon Oct 12, 2015 10:10 am ] |
| Post subject: | |
Have you ever put a rebuild kit on the carb? Fairly easy 1-3 hour job depending how much of a handyman are you. |
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| Author: | ddonner [ Mon Oct 12, 2015 10:54 am ] |
| Post subject: | reply |
Partially did so when I cleaned the carb. I didn't replace the pump diaphram assembly or the pump lever bushing, but I did blow out all the passageways I could find with carb cleaner and the Cuda accelerates nicely when I pump the accelerator. (and then the engine dies when I brake). |
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| Author: | Jsp [ Tue Oct 13, 2015 5:40 am ] |
| Post subject: | Re: reply |
Quote: Partially did so when I cleaned the carb. I didn't replace the pump diaphram assembly or the pump lever bushing, but I did blow out all the passageways I could find with carb cleaner and the Cuda accelerates nicely when I pump the accelerator. (and then the engine dies when I brake).
Any play on the throttle plate shaft? |
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| Author: | Reed [ Tue Oct 13, 2015 7:25 am ] |
| Post subject: | |
Have you verified the adjustment and integrity of the float? |
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| Author: | wjajr [ Tue Oct 13, 2015 11:24 am ] |
| Post subject: | |
Fuel pump may not be delivering fuel at full volume and pressure due to some crud from tank impeding its function. This would effect fuel level in bowl, and drivability at highway speeds. There could be another load of crud forming in carburetor because the fuel pick-up sock has become detached, or has been compromised with holes. |
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| Author: | mvh [ Fri Oct 16, 2015 2:45 pm ] |
| Post subject: | Similar problem |
I have a Holley 1920 in a 67 Barracuda with a similar problem. It dies under braking or at idle. It does not have a "crud" problem or any problems at speed, and I just installed a rebuild kit. I suspect you had two separate issues. The most common suggestion I have been hearing is that it's caused by a vacuum leak. This could be at the manifold gasket, the carb base gasket, or at the throttle shaft. Since I have been experiencing a persistent exhaust leak at the manifold gasket, I suspect that's my culprit (same gasket). On that subject, does anyone have any advice on which type of manifold gasket to use? the stamped metal type, or a composition gasket? One other possibility on my carb is the idle mixture screw hole. At some point someone overtightened it so that the needle created a bulge in the inner wall of the carb throat, with a hairline crack in the zinc. So this could be my air leak. The only cure for this would be a new carb body. |
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| Author: | ddonner [ Sat Oct 17, 2015 5:49 pm ] |
| Post subject: | Now OK after 2nd cleaning/rebuild |
Well, at the forum's encouragement, I tore the 1920 apart again and redid the cleaning. Much to my surprise there Was additional crud that came out. (Incidently, on the tank pickup sock comment, I had reciently pulled the tank and replaced the pickup/sending unit maybe a year ago. I also blew out the lines during the 1st rebuild (and they did have crud) and replaced the fuel pump and filter. And I'm keeping watch on the filter religiously.) Surprised by the additional crud, I kept soaking and cleaning and blowing internal passages until I was Certain that nothing more had come out for two more attempts. Then I put her back together with the few new rebuild parts that I had not previously replaced. And success. She seems to be back to running like she should be running. So thanks guys. I appreciate you. Don |
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| Author: | wjajr [ Sun Oct 18, 2015 6:34 am ] |
| Post subject: | |
You may have to continue to decrud fuel system several more times before it cleans up. Sometimes there is crap stuck to inside of fuel lines that will continue to dislodge/dissolve over time, as well as rust and the same crap clinging to internal tank surfaces that first cleaning didn't remove. Keep a spare fuel filter in glove box next to your back-up ballast resistor. |
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