Carburetors Carb discussion and questions. Upgrading your Third Gen's carburetor, swapping TBI to carburetor, or TPI to carburetor? Need LG4 or H.O. info? Post it here.

carb too big?

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Old Feb 3, 2014 | 10:20 AM
  #1  
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Car: firebird 91
Engine: 350 5.7 small block
Transmission: turbo transmission
carb too big?

I had a mechanic I know just take a quick look he said all is good under ur hood accept your carb is way to big and it is sucking all yout gas up and that it'll eventually burn your engine cause its pushin 10-20 when it should be around 5-6psi so its a demon carb I guess some have no numbers to identify so should I downgrade?
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Old Feb 3, 2014 | 01:20 PM
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Car: 1983 Z28
Engine: 385 Fastburn
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Axle/Gears: BorgWarner 9-bolt posi, 3.27 gears
Re: carb too big?

Please. please. use punctuation.

There are no numbers whatsoever on the carb?
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Old Feb 3, 2014 | 02:33 PM
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Car: firebird 91
Engine: 350 5.7 small block
Transmission: turbo transmission
Re: carb too big?

Sorry no numbers,this is it right herehttp://thumbs3.ebaystatic.com/d/l225/m/mhUAuCaOX0K28gxdCHXqpOA.jpg
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Old Feb 3, 2014 | 02:45 PM
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From: Louisville, KY
Car: 1983 Z28
Engine: 385 Fastburn
Transmission: T-5
Axle/Gears: BorgWarner 9-bolt posi, 3.27 gears
Re: carb too big?

Give this a shot:

http://www.demoncarbs.com/Assets/doc...tity-Speed.pdf
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Old Feb 3, 2014 | 03:10 PM
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midias's Avatar
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From: Henrietta NY
Car: 1984 Trans Am L69
Engine: Sniper EFI Powered 355
Transmission: WC T5 w/ Steel Support Plate
Axle/Gears: 3.42 10 Bolt Posi
Re: carb too big?

So your pushing 10-20 psi into your carb? Do you have a regulator on it?

We need to know what carb you have before we can tell you if it is too big. Just stating the brand does not help. They make more than one. It is the Jegs 350 allover again.
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Old Feb 3, 2014 | 10:08 PM
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Car: 1991 Firebird convertible
Engine: LQ4 ls 6.0
Transmission: 4L60E
Axle/Gears: 342 Limited slip
Re: carb too big?

Also what have you done to the engine heads-cam-intake-exhaust??
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Old Feb 3, 2014 | 10:19 PM
  #7  
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Car: 1984 Trans Am L69
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Transmission: WC T5 w/ Steel Support Plate
Axle/Gears: 3.42 10 Bolt Posi
Re: carb too big?

Originally Posted by Mirror Image
Also what have you done to the engine heads-cam-intake-exhaust??

its the pos Jegs "260" hp goodwrench 350

Last edited by midias; Feb 4, 2014 at 07:25 AM.
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Old Feb 3, 2014 | 10:46 PM
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Car: 1991 Firebird convertible
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Axle/Gears: 342 Limited slip
Re: carb too big?

I would say yeah thats to big for a 260HP engine without a part # its hard to say it looks like the 750 double pumper with mechanical secondaries
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Old Feb 4, 2014 | 07:02 AM
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Re: carb too big?

it seems to be a point of contention around here but in my racing experience the guys with 350's under 300-350hp run good with 650cfm and over that some upper end power is gained by going to 750. more important than size though is proper tuning, there is a pretty good write up in this section on tuning the holley dp which i believe would be similar. and if you have 20 psi going to your carb you need a regulator and adjust it to 5-6, for all carbs no matter the size or brand
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Old Feb 4, 2014 | 07:26 AM
  #10  
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Car: 1984 Trans Am L69
Engine: Sniper EFI Powered 355
Transmission: WC T5 w/ Steel Support Plate
Axle/Gears: 3.42 10 Bolt Posi
Re: carb too big?

A 650 will support a 400hp 350 without any issues
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Old Feb 4, 2014 | 09:30 AM
  #11  
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Car: 1983 Z28
Engine: 385 Fastburn
Transmission: T-5
Axle/Gears: BorgWarner 9-bolt posi, 3.27 gears
Re: carb too big?

Originally Posted by midias
its the pos Jegs "260" hp goodwrench 350
I am a little confused. patriots781 is the OP, so do you actually know his engine or was this just some random guess?

and just my 2 cents: my 350 loves it's holley 750 dp (though it is properly tuned)
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Old Feb 4, 2014 | 09:33 AM
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Car: 1984 Trans Am L69
Engine: Sniper EFI Powered 355
Transmission: WC T5 w/ Steel Support Plate
Axle/Gears: 3.42 10 Bolt Posi
Re: carb too big?

Originally Posted by RedLeader289
I am a little confused. patriots781 is the OP, so do you actually know his engine or was this just some random guess?

and just my 2 cents: my 350 loves it's holley 750 dp (though it is properly tuned)
Refer to this train wreck

https://www.thirdgen.org/forums/afte...ods-350-a.html
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Old Feb 4, 2014 | 10:27 AM
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Car: 1983 Z28
Engine: 385 Fastburn
Transmission: T-5
Axle/Gears: BorgWarner 9-bolt posi, 3.27 gears
Re: carb too big?

Originally Posted by midias
oh...just...wow...

Well then. patriots781, have you used the .pdf I posted to ID your carb yet?
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Old Feb 4, 2014 | 06:10 PM
  #14  
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Car: firebird 91
Engine: 350 5.7 small block
Transmission: turbo transmission
Re: carb too big?

Ya it wont download on my phone,but I appreciate the good advice seems to be mixed opinions and ya its the 260 hp one, so point get a regulator.......keep posting a link to other threads cause you sit behind your keyboard like a internet tough guy if your not gonna offer any good usable advice don't post you can't give any you just post whatever stupid b.s or question you can you don't give any good advice sorry you were teased or bullied don't take it out on my post tough guy sorry its 2014 if you can't understand abrev. That's your own problem damn......thanks to everyone else
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Old Feb 4, 2014 | 08:03 PM
  #15  
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From: Henrietta NY
Car: 1984 Trans Am L69
Engine: Sniper EFI Powered 355
Transmission: WC T5 w/ Steel Support Plate
Axle/Gears: 3.42 10 Bolt Posi
Re: carb too big?

Download this and read the PDF for android devices

https://play.google.com/store/apps/d...e.reader&hl=en

Cannot help this kid. Someone asked how I knew it was a 260HP I posed how I knew. It is called a reference, anyone who has written a proper report would know that.

It is 2014 with auto correct and android you should be able to swipe faster that using abbreviations that make your posts resemble a chimp sitting on a keyboard.

You don't take the time to write intelligible sentences or questions then you bitch when people cannot help you. You don't even take the time to post in the proper forums. You are asking us for help, we asked you to read what you wrote before posting. Instead you whine like some spoiled kid without a clue. I have offered you damn good advice you refuse to take. You seem to want to jump right in without having any clue. This will lead to wasted time and money, in the end your combo will not be anything near what you want it to be. Considering I have done your exact build I could have been a fair amount of help.

I am done no more help for you. It is not worth my time trying to figure out if you are making a statement or asking a question.


Last edited by midias; Feb 4, 2014 at 09:13 PM.
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Old Feb 6, 2014 | 02:57 PM
  #16  
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From: sussex county, NJ
Car: 84 Z28 / 11 genesis coupe
Engine: 355/210 heads/275deh/Proform 750 DP
Transmission: 700r4/B&M 2400
Axle/Gears: 02, allu.axle, 3.42, posi
Re: carb too big?

strange how do you get 20 psi fuel pressure on the carburetor and it didn't blew up the needle/ seat yet. Anyway if the needle is still doing it's job having higher pressure doesn't mean you use more fuel it just a risk of damaging the carburetor.
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Old Feb 11, 2014 | 09:03 PM
  #17  
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From: Sanctuary state
Car: 67 ******mobile
Engine: 385 Solid roller
Transmission: T-56
Axle/Gears: 4.11
Re: carb too big?

Originally Posted by midias
A 650 will support a 400hp 350 without any issues

had a 430hp that was always lacking "something" with a few 750s tuned every which way from Sunday

Stuck a friends well sorted out 650 on it and the car couldnt keep the tires planted. Night and day difference, bigger isnt always better.
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Old Feb 12, 2014 | 07:13 AM
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Car: 87 bird
Engine: enough to break stuff
Transmission: manual th400
Axle/Gears: 4.10
Re: carb too big?

yours was not tuned properly if it made that big a difference.
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Old Feb 18, 2014 | 04:45 PM
  #19  
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Car: firebird 91
Engine: 350 5.7 small block
Transmission: turbo transmission
Re: carb too big?

Ok,it's 800 cfm demon carb 2 barrel w/edelbrock intake my buddy is my mechanic he said to swap it out for a smaller one,I mean I plan to mod put a cam,heads,New intake in in near future so I was just gonna keep it in though.again I have a 350/260 hp got 882 heads bbk long tube headers,true dual straight pipe exhaust...Any thoughts?
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Old Feb 18, 2014 | 05:35 PM
  #20  
midias's Avatar
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From: Henrietta NY
Car: 1984 Trans Am L69
Engine: Sniper EFI Powered 355
Transmission: WC T5 w/ Steel Support Plate
Axle/Gears: 3.42 10 Bolt Posi
Re: carb too big?

Originally Posted by patriots781
Ok,it's 800 cfm demon carb 2 barrel w/edelbrock intake my buddy is my mechanic he said to swap it out for a smaller one,I mean I plan to mod put a cam,heads,New intake in in near future so I was just gonna keep it in though.again I have a 350/260 hp got 882 heads bbk long tube headers,true dual straight pipe exhaust...Any thoughts?
I don't think demon makes an 800cfm 2 barrel carb. I know at one point they made a 2 barrel 350 and 500cfm carb.

The 500 would probably be great on your engine.

Chances are no matter what you do to a 350 short of forced induction you will NOT need an 800cfm carb.
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Old Feb 18, 2014 | 06:17 PM
  #21  
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Car: firebird 91
Engine: 350 5.7 small block
Transmission: turbo transmission
Re: carb too big?

Here's some pics
Attached Thumbnails carb too big?-securedownload-29.jpeg   carb too big?-securedownload-37.jpeg   carb too big?-securedownload-22.jpeg  
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Old Feb 18, 2014 | 06:18 PM
  #22  
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Car: firebird 91
Engine: 350 5.7 small block
Transmission: turbo transmission
Re: carb too big?

Pics
Attached Thumbnails carb too big?-securedownload-31.jpeg   carb too big?-securedownload-19.jpeg  
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Old Feb 18, 2014 | 06:48 PM
  #23  
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From: Spring Hill, Fl.
Car: 87 iroc-z
Engine: 454
Transmission: th350
Axle/Gears: 3.73
Re: carb too big?

looks like a 4 barrel, double pumper.
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Old Feb 18, 2014 | 06:56 PM
  #24  
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From: Henrietta NY
Car: 1984 Trans Am L69
Engine: Sniper EFI Powered 355
Transmission: WC T5 w/ Steel Support Plate
Axle/Gears: 3.42 10 Bolt Posi
Re: carb too big?

100% sure that is a 4 barrel demon carb. Not sure if it a 800cfm. All I know is it is WAY to big for that engine at 800.

Also you have stamp steel rockers you could do roller rockers as an upgrade.
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Old Feb 18, 2014 | 07:07 PM
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From: Birmingham Alabama
Car: 1991 Firebird convertible
Engine: LQ4 ls 6.0
Transmission: 4L60E
Axle/Gears: 342 Limited slip
Re: carb too big?

I think a 750 Qjet would work good they have great driveability better gas miliage
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Old Feb 19, 2014 | 08:19 AM
  #26  
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From: Henrietta NY
Car: 1984 Trans Am L69
Engine: Sniper EFI Powered 355
Transmission: WC T5 w/ Steel Support Plate
Axle/Gears: 3.42 10 Bolt Posi
Re: carb too big?

Originally Posted by Mirror Image
I think a 750 Qjet would work good they have great driveability better gas miliage
Agreed, although if you want to stay demon a nice street demon carb in the 600cfm range would work and still support a bigger cam and heads.
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