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 Building Q-jet for mild 350 in daily driver 
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Joined: Tue Aug 23, 2016 10:38 am
Posts: 84
I bought a 74 Malibu "crew cab" to drive everyday and to take to cruise night etc since the car seat doesn't fit in my Camaro, esp with the bar.

Currently it has 30k mile original L-65 2bbl 8.5 to 1 350. Over the winter it will get a cam (214/224 112lsa) , performer intake, headers and duals in addition to a q-jet. Hoping to of course make more power but since it is a daily I am trying to squeeze mpg out of it too.

Like I said in my other threads I am buddies with a local machine shop that has quite a few q-jet cores so they are selling me 4 for $50. So far I found 2 chevy carbs on friday and actually picked up a BOP carb this morning I may use as a donor for a few parts (has the main air bleed brass restrictors).

Attached is the specs of the 2 carbs I got Saturday on the 77 cruiser sheet.

I guess I assumed moving the idle air bleed was a good idea and reducing the main circuit air bleeds is suggested.

Where would you start on the main system air bleeds?

Same size idle air bleed as what was in the bore after you move it to the lid?

I have no problem drilling out the down channel restrictor and tapping it because it will also help block the bleed but what size would you recommend?

Do I need to do the tube too? I am bit intimidated about making my own screw in tubes but I guess I have more than a few to mess up.

I know tuner says the secondary mod is great for everything, but even a daily?

Like everyone I want it to make eleventy billion horsepowers and 50 mpg but I know there is compromises on everything. I just want it to run good, like I now these can, and start getting a good handle on how these work so I can put a q-jet on the big block I am slowly building for this.

Thanks for all the help thus far. Sorry I am so green.

John


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Mon Sep 12, 2016 8:40 am
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Joined: Sat Aug 24, 2013 7:57 pm
Posts: 152
Location: Frostburg, MD
80427 wrote:

snipped

Do I need to do the tube too? I am bit intimidated about making my own screw in tubes but I guess I have more than a few to mess up.



John, pretty green here too, but once you have the idle tubes out, it's cake. I admire the guys that dyi them, but it is too easy for a one or two carb guy to buy them. Unless someone has a source for them with 10-32, these are the only option that I've found at $11 per pair. They are 10-48, straight screwdriver slot, not hex.

viewtopic.php?f=26&t=1236

If you need a 10-48 tap, I have some extras, usa made, send me $6 and I'll mail you one. He wants like $35 more with a tap.

He has reasonably priced air horn gaskets too. Best to get a few, as it'll be off a few times.

http://www.allcarbs.com/catlist.php

Dave


Last edited by dave brode on Mon Sep 12, 2016 4:20 pm, edited 1 time in total.



Mon Sep 12, 2016 4:10 pm
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Joined: Tue Aug 23, 2016 10:38 am
Posts: 84
I guess they could have been messed with but the amount of dirt and grease these carbs had on them leads me to believe they at least predate the "stage xyz" book. I was surprised how big the idle feed tubes and restrictions were compared to Tuners suggestions.

I will pull apart and measure the bop carb tonight for fun. At least it gives me another source for parts.


Mon Sep 12, 2016 4:20 pm
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Joined: Sat Aug 24, 2013 7:57 pm
Posts: 152
Location: Frostburg, MD
80427 wrote:
I was surprised how big the idle feed tubes and restrictions were compared to Tuners suggestions.

I will pull apart and measure the bop carb tonight for fun. At least it gives me another source for parts.


My '76 carb had a .033" idle tube. Tuner states that the newer vehicles could not run leaner than stoich, so the cat-cons would function. viewtopic.php?f=26&t=1274

I suspect that the 70s truck carbs had such large MABs so they would not get much richer than stoich under heavy throttle. Maybe GM felt that it was ok for the newer cars to go a tad richer, as they would not see WOT for long periods, like trucks.


Mon Sep 12, 2016 4:40 pm
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Joined: Wed Oct 23, 2013 8:01 am
Posts: 108
Hey ya stole my sheet, I feel special.


Mon Sep 12, 2016 6:05 pm
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Joined: Tue May 06, 2014 5:34 pm
Posts: 42
77cruiser wrote:
Hey ya stole my sheet, I feel special.


anyone messing with a Quadrajet is special... :roll:


Mon Sep 12, 2016 9:30 pm
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Joined: Tue Aug 23, 2016 10:38 am
Posts: 84
Like short bus special?


Mon Sep 12, 2016 11:01 pm
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Joined: Fri Feb 08, 2013 2:37 pm
Posts: 1701
If it has a QJet on it, the bus is special too.


Mon Sep 12, 2016 11:32 pm
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Joined: Tue Aug 23, 2016 10:38 am
Posts: 84
So since a tore apart all my spare q-jet looking for parts I have plenty of down channel restrictions and actually think I can pull the lower air bleed from the olds carb. What size would you really make them, or at least start at? .46-.070 seems like a big range when I am used to changing the by the .005s.


Mon Sep 12, 2016 11:43 pm
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Joined: Fri Feb 08, 2013 2:37 pm
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.046"


Mon Sep 12, 2016 11:44 pm
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