Holley 670 vacuum secondary running like dog crap
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Holley 670 vacuum secondary running like dog crap
I know this is a bit broad of a question but it's on my 89 third gen and there's some pretty knowledgeable people on here so I figure why not. Over a year ago I swapped a truck 350 in my car, originally a tbi 305 and it had been a huge headache ever since I could never get the tbi to run right. So I finally decided after doing the top end with some flowtek 180cc heads and an edelbrock dual plane to drop a carb on. It's a 670 with electric choke and vacuum secondaries. Idles a bit rough and when you put the throttle all the way to the floor it literally blows fuel onto the windshield. I'm running an hei and the timing is alright. The idle air mixture screws were one turn away from being all the way in. I'm new to this and have no idea where to start tuning on it. You can literally hear a popping noise coming from inside the intake when you give it more than half throttle. Any ideas of where to start? Ps I forgot to mention I am just using the stock fuel pump with a return style regulator from holley, through the sight glasses it looks like everything on fuel delivery to the carb is where it should be
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Joined: Sep 2002
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From: honolulu
Car: '86MCSS
Engine: 396 .030"
Transmission: M20
Re: Holley 670 vacuum secondary running like dog crap
There is no mention of installing a vacuum advance distributor. If you swapped to a carb, you're going to need it.
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Re: Holley 670 vacuum secondary running like dog crap
Member
Joined: Sep 2002
Posts: 253
Likes: 25
From: honolulu
Car: '86MCSS
Engine: 396 .030"
Transmission: M20
Re: Holley 670 vacuum secondary running like dog crap
Hey you did mention HEI but my C4 has an HEI as well but no vacuum advance. All done by the computer...
Carbs don't need a whole lot of pressure but one can only assume that's been addressed with the Holley fpr. Do you know what the actual pressure that is being supplied to the carb? Anything excess of 6-7 psi can unseat the needles in the float and can cause flooding. I suppose when you set the float, if nothing is dumping out, you're fine. Mixture screws, all the way in and 1-1.5 turns out is a good starting point and you back it out for best idle quality and highest vacuum attained.
I'm not totally convinced that your timing is right and the mere fact that you don't say what you set it at or what it is at higher rpms raises questions. Maybe you already know this so I apologize for dumbing it down. Think about the ignition event on a timeline. Imagine the fuel traveling through the carb, intake, past the intake valve into the combustion chamber, out the exhaust valve and exhaust. Light the fire too early or advanced and it goes bang out the carb or intake. Light the fire too late during the ignition event or retarded and it goes bang in the exhaust pipe. Also keep in mind in the combustion process, fuel ignites at the same rate. At lower rpms you can get away with less advance but as the engine speeds up, you need to light that fire earlier.
A---------------------TDC-----------------------R
Carbs don't need a whole lot of pressure but one can only assume that's been addressed with the Holley fpr. Do you know what the actual pressure that is being supplied to the carb? Anything excess of 6-7 psi can unseat the needles in the float and can cause flooding. I suppose when you set the float, if nothing is dumping out, you're fine. Mixture screws, all the way in and 1-1.5 turns out is a good starting point and you back it out for best idle quality and highest vacuum attained.
I'm not totally convinced that your timing is right and the mere fact that you don't say what you set it at or what it is at higher rpms raises questions. Maybe you already know this so I apologize for dumbing it down. Think about the ignition event on a timeline. Imagine the fuel traveling through the carb, intake, past the intake valve into the combustion chamber, out the exhaust valve and exhaust. Light the fire too early or advanced and it goes bang out the carb or intake. Light the fire too late during the ignition event or retarded and it goes bang in the exhaust pipe. Also keep in mind in the combustion process, fuel ignites at the same rate. At lower rpms you can get away with less advance but as the engine speeds up, you need to light that fire earlier.
A---------------------TDC-----------------------R
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Joined: Oct 2021
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Re: Holley 670 vacuum secondary running like dog crap
Hey you did mention HEI but my C4 has an HEI as well but no vacuum advance. All done by the computer...
Carbs don't need a whole lot of pressure but one can only assume that's been addressed with the Holley fpr. Do you know what the actual pressure that is being supplied to the carb? Anything excess of 6-7 psi can unseat the needles in the float and can cause flooding. I suppose when you set the float, if nothing is dumping out, you're fine. Mixture screws, all the way in and 1-1.5 turns out is a good starting point and you back it out for best idle quality and highest vacuum attained.
I'm not totally convinced that your timing is right and the mere fact that you don't say what you set it at or what it is at higher rpms raises questions. Maybe you already know this so I apologize for dumbing it down. Think about the ignition event on a timeline. Imagine the fuel traveling through the carb, intake, past the intake valve into the combustion chamber, out the exhaust valve and exhaust. Light the fire too early or advanced and it goes bang out the carb or intake. Light the fire too late during the ignition event or retarded and it goes bang in the exhaust pipe. Also keep in mind in the combustion process, fuel ignites at the same rate. At lower rpms you can get away with less advance but as the engine speeds up, you need to light that fire earlier.
A---------------------TDC-----------------------R
Carbs don't need a whole lot of pressure but one can only assume that's been addressed with the Holley fpr. Do you know what the actual pressure that is being supplied to the carb? Anything excess of 6-7 psi can unseat the needles in the float and can cause flooding. I suppose when you set the float, if nothing is dumping out, you're fine. Mixture screws, all the way in and 1-1.5 turns out is a good starting point and you back it out for best idle quality and highest vacuum attained.
I'm not totally convinced that your timing is right and the mere fact that you don't say what you set it at or what it is at higher rpms raises questions. Maybe you already know this so I apologize for dumbing it down. Think about the ignition event on a timeline. Imagine the fuel traveling through the carb, intake, past the intake valve into the combustion chamber, out the exhaust valve and exhaust. Light the fire too early or advanced and it goes bang out the carb or intake. Light the fire too late during the ignition event or retarded and it goes bang in the exhaust pipe. Also keep in mind in the combustion process, fuel ignites at the same rate. At lower rpms you can get away with less advance but as the engine speeds up, you need to light that fire earlier.
A---------------------TDC-----------------------R
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From: South FL
Car: 1989 Formula T-Top
Engine: 350 TPI, twin turbo
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Axle/Gears: 3.23
Re: Holley 670 vacuum secondary running like dog crap
I bought a new in sealed box Holly one time and I could not get it tuned, I finally took it apart and found the secondaries float had a hole in it and the float was full of gas. I guess you would call that a sink not a float. Maybe there is some little piece of junk in your carb someplace?
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