Vacuum pressure

1987 CHEVROLET TRUCK
30,000 MILES • 5.7L • V8 • 2WD • AUTOMATIC
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Okay, so I have a Holley 670 CFM that I just installed on my 350 engine. I am trying to set my idle mixture screws at the right point. I went and bought a vacuum gauge today to help with the process tomorrow. I was looking on YouTube and it says to place it on the highest vacuum point. Is this true? Or is there a specific point where it should be. The reason this needs to be done is because I know I am running rich because I have small fuel spray coming out of the exhaust.
Aug 15, 2017 at 5:23 PM
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So I tired to set it. But I feel as though I am not doing it right. I still have black smoke coming out the exhaust. I pulled the plugs and replaced them as well today. They were covered with black soot and they smelled like some fuel as well.
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Aug 16, 2017 at 7:16 PM
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STEVE W.
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Which Holley do you have? Post the part number so we have a starting point. From the description you have jets that are far to large in it. Is the engine stock or? That can change things a lot. A 670 is going to come from the factory with jets that are large for a stock 350 in a truck. A 600 would be about right on a stock small block.
Post what you have and we can go from there.
Aug 16, 2017 at 7:32 PM
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Here is my part number.
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Aug 17, 2017 at 4:55 PM
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STEVE W.
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Are you running a factory stock engine and fuel pump?
Also have you called Holley tech support, they are REALLY good for helping in this type of situation. 1-866-464-6553
Aug 17, 2017 at 5:47 PM
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I believe everything is stock. I bought it as is. I have not called Holley support yet.
Aug 17, 2017 at 7:59 PM
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Okay so it was the jet and master valve size it was to big for the engine size. They had 6.5 from factory. So I installed my old carburetor (less performance) it had 7.2 and I replaced it with the 6.5 jets and bammm no smoke. I just ordered new jets for my new Holley Avenger 670, once they come in I will reinstall the new carburetor and give y'all an update.
Aug 18, 2017 at 1:18 PM
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STEVE W.
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Yep, the description said large jets. Holley makes a good cab, but I still like the old Q-Jet. Properly set up they will give better mileage and if you use the larger units you can make them really perform when those garbage can lids open up...
Aug 18, 2017 at 11:42 PM