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PostPosted: Wed May 25, 2016 5:14 pm 
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Turbo Slant 6
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Joined: Fri Dec 30, 2005 2:49 pm
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Location: Houston, TX
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Still trying to get my art car roadworthy. It's a 64 Dart with a 225 and a Holley 1920. I believe the carb was a remanufactured unit (I know...), but I got it from the same friend who I got the engine from, and it was reportedly running fine before we pulled the engine from the donor car a year and a half ago.

The engine behaves like it has a big vacuum leak. When hot, it will only stay running with the choke engaged. It won't run at all below ~1500 RPM, and the required amount of choke to keep it running drops off with higher RPM. I checked everywhere with a can of starting fluid and can't find a leak, including carb base, vacuum lines, and intake manifold to head connection. Blocking off the PCV line helps a little, but not enough. Either I'm missing a big source of unmetered air, or its just not getting enough fuel in the main circuit. I took the bowl off, and everything looked clean. No obvious gunk. The main jet was clear. I tried stepping up two jet sizes and it didn't make much difference, if any. There may be a clog somewhere deeper in the carb, but who knows where. I installed a new fuel filter before firing it up the first time, but I'm not sure how old the gas in the tank is.

The kicker is that it was behaving fine in the garage yesterday (in neutral). Then when I was idling it today to check the trans fluid, it suddenly died and started exhibiting the above symptoms upon restart. The only thing I know that has changed in the last day or so is the exhaust manifold choke stove broke, but I'm not sure if it was even working properly before. I don't recall the engine running with very much choke engagement before that. You don't just develop a huge vacuum leak that suddenly, and I can't find a vacuum leak anyway, so I'm thinking something in the main fuel circuit became partially clogged.

I was planning to take this thing on a road trip this weekend. Anything else I should check before tearing this carb apart?

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PostPosted: Wed May 25, 2016 5:41 pm 
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SpaceFrank wrote:
It won't run at all below ~1500 RPM, and the required amount of choke to keep it running drops off with higher RPM. (…) Either I'm missing a big source of unmetered air, or its just not getting enough fuel in the main circuit


The main circuit sounds fine; it's the idle circuit you should be suspecting.

Quote:
I took the bowl off


Hope you've got a new bowl gasket to reinstall it with, otherwise odds are excellent of a fuel leak right over the hot manifolds. While the carb is open, take off the upsized main jet and put the other one back in.

Once the bowl is back on, do these things:

-look down the carb and find the two holes, one small and one real small, facing the sky next to the front wall of the carb throat. Blast each hole with carburetor cleaner -- put the straw directly on the hole and spray for several seconds.

-Manually put the fast-idle cam in place and tighten the fast-idle screw so it'll hold the throttle open enough for the engine to run at a very fast idle. Start it. Close the choke as much as you can without killing the engine. With the engine running, remove the idle mixture needle. You may need a quick hand on the choke to keep the engine running once the needle's out. Blast the carburetor cleaner in through the idle mixture needle hole. Keep spraying and spraying; you may have to spray in bursts to keep from stalling the engine. The idea is to flush the trash out of the idle circuit. When you're done (or you run out of carb spray), shut off the engine. Reinstlal the mixture needle, lightly(!) seat it, back it off three full turns and then turn it back in 1/2 turn. Un-tighten the fast idle screw back to where it belongs, open the choke, and drop the fast idle cam out. Now see if it'll idle. If so, adjust the idle mixture and speed to where they should be.

(Use a good brand of carb spray; I prefer Berryman's Chemtool B12. Also, give a few shots around the idle mixture needle before removing it so you won't be blowing trash into the idle circuit.)

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PostPosted: Thu May 26, 2016 11:26 am 
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Turbo Slant 6
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Joined: Fri Dec 30, 2005 2:49 pm
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Location: Houston, TX
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I don't know why I didn't suspect the idle circuit. Did I mention I got 2 hours of sleep the night before I wrote this? :oops:

Thanks for the guidance on cleaning, Dan. I'll pick up a can of B-12 on my way home from work.

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Somehow I ended up owning three 1964 slant six A-bodies. I race one of them.
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PostPosted: Thu May 26, 2016 8:07 pm 
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Turbo Slant 6
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Location: Houston, TX
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Well, that did it. Thanks! It runs fine now.

I swapped the other jet back in, but the bowl gasket appears to be in good shape and isn't leaking yet. I went ahead and ordered one just in case.

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Somehow I ended up owning three 1964 slant six A-bodies. I race one of them.
Escape Velocity Racing


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PostPosted: Thu May 26, 2016 8:08 pm 
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Hoorah for easy fixes! Bring that can of B12 along with you.

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Too many people who were born on third base actually believe they've hit a triple.

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PostPosted: Fri Jun 10, 2016 10:13 pm 
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Joined: Wed May 18, 2016 6:07 am
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Location: Vancouver, Wa
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I recently rebuilt my 1920 carb. Before I did it I didn't have a vacuum leak. Now it looks like I have one where the throttle shaft goes into the body. After I rebuilt the carb I also noticed that I have an oring that wasnt in the kit and did not get replaced. It looks like a small rubber band. Any idea where it goes? Are my two problems related?


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