Vacuum pressure

Tiny
NONLIMITSOLDIER
  • MEMBER
  • 1987 CHEVROLET TRUCK
  • 5.7L
  • V8
  • 2WD
  • AUTOMATIC
  • 30,000 MILES
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.
Tuesday, August 15th, 2017 AT 5:23 PM

7 Replies

Tiny
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  • MEMBER
  • 7 POSTS
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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Wednesday, August 16th, 2017 AT 7:16 PM
Tiny
STEVE W.
  • MECHANIC
  • 15,237 POSTS
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.
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Wednesday, August 16th, 2017 AT 7:32 PM
Tiny
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Here is my part number.
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Thursday, August 17th, 2017 AT 4:55 PM
Tiny
STEVE W.
  • MECHANIC
  • 15,237 POSTS
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
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Thursday, August 17th, 2017 AT 5:47 PM
Tiny
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I believe everything is stock. I bought it as is. I have not called Holley support yet.
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Thursday, August 17th, 2017 AT 7:59 PM
Tiny
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  • MEMBER
  • 7 POSTS
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.
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Friday, August 18th, 2017 AT 1:18 PM
Tiny
STEVE W.
  • MECHANIC
  • 15,237 POSTS
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.
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Friday, August 18th, 2017 AT 11:42 PM

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