Need help please, Rochester jet settings ?????
Thread Starter
Race Director
Joined: Aug 2007
Posts: 10,977
Likes: 19
From: Canboro Ontario
Need help please, Rochester jet settings ?????
I have a 73 454 with 400 turbo tranny with a/c. What would be the setting for a Quadrajet. There are two jets, I believe, which I am not sure which is which. Could someone please let me know, what the settings would be for each and which one is which. Thank you.
Thread Starter
Race Director
Joined: Aug 2007
Posts: 10,977
Likes: 19
From: Canboro Ontario
I have no idea what that means. I thought it was like so many turns, like 1 1/4 or something. How do you get Lars papers ? and will I be able to understand ???
Race Director
Joined: Jan 2000
Posts: 12,399
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From: San Jose CA
Be careful throwing random jets and rods at a carburetor. First off, you need to match the jet to the casting number, ASSUMING the carburetor hasn't been tweaked.
If its been tweaked, all bets are off.
In carburetor speak, a jet is an orifice with conical inlet and outlet that measures a metered amount of fuel. Larger jets richen the mixture, smaller lean. Rods are the opposite as they restrict fuel flow through the jets.
HTH.
If its been tweaked, all bets are off.
In carburetor speak, a jet is an orifice with conical inlet and outlet that measures a metered amount of fuel. Larger jets richen the mixture, smaller lean. Rods are the opposite as they restrict fuel flow through the jets.
HTH.
Race Director
Joined: Apr 2011
Posts: 11,183
Likes: 3,335
From: North of Toronto - Ontario
Anyway, email Lars for all your Q-jet info
v8fastcars@msn.com
HIH
M
Burning Brakes
Joined: Dec 2012
Posts: 1,243
Likes: 19
From: Edmond Oklahoma
Lars is awesome. He sent me Q-jet tuning document. Everything you need to know.
Better yet if you got problems or unknowns. Send it to him to match up with your engine I.e. Check everything out spec wise
Last edited by donbayers; Jun 27, 2014 at 12:14 AM.
Thread Starter
Race Director
Joined: Aug 2007
Posts: 10,977
Likes: 19
From: Canboro Ontario
I'm thinking maybe you mean the mixture screws at the front?
Anyway, email Lars for all your Q-jet info
v8fastcars@msn.com
HIH
M
Anyway, email Lars for all your Q-jet info
v8fastcars@msn.com
HIH
M
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Race Director
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turn them out about 2 full turns from fully seated and then set the idle speed screw on the side of the carburetor to your desired speed. Then starting with either mixturen screw turn it in 1/4 turn at a time till you notice an rpm drop when you get a drop go back out 1/4 turn. Then do the same with the other screw.
Le Mans Master
Joined: Jul 2006
Posts: 8,117
Likes: 104
From: charlotte north carolina
The idle screws are closed? Did the engine run with this setting? If it did, the carb "rebuild" is highly suspicious. BTW, Lars recommends 74-41 jet/rod values for BBC with CH secondary rods. I can attest that these numbers work very well.
Thread Starter
Race Director
Joined: Aug 2007
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From: Canboro Ontario
There is no gas getting into the carb. All I did was switch the two carbs, The first carb was working fine, but I wanted to switch, just for the numbers thing. I don't understand why no gas is getting into the carb. I have adjusted the mixture screws as posted, but still no gas.
Race Director
Joined: Apr 2011
Posts: 11,183
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From: North of Toronto - Ontario
I've only stumbled my way through my own carb a few years back (with help from Lars and a book by Cliff R which only showed up afterwards...) but here's maybe a starting point
If the float is stuck (or the little plunger fuel valve disconnected inside it won't let any fuel into the carb) since it would think the bowl is already full.
Also, If it's got one of those paper filters with the anti-drain back rubber flap bit and it's in backwards somehow.........
Anyway, I'm sure someone who actually knows something will be along shortly
M
If the float is stuck (or the little plunger fuel valve disconnected inside it won't let any fuel into the carb) since it would think the bowl is already full.
Also, If it's got one of those paper filters with the anti-drain back rubber flap bit and it's in backwards somehow.........
Anyway, I'm sure someone who actually knows something will be along shortly
M
Racer
Joined: Apr 2012
Posts: 464
Likes: 1
From: Austell Georgia
I apologize if I'm going to seem to oversimplify.
On the idle screws, close them, clockwise, until they just seat and the open the 1 to 1 1/2 turns each to get started.
I'll assume there is fuel in the tank and the pump is operating since it did before....at least for now
Add fuel through the vent at the top of the carb. You need a really small funnel or be creative. Don't know how much but maybe 1/4 cup or so?
Activate the throttle and see if you get fuel. Maybe the carb is just not getting a prime to it. If you see fuel, try to start and we'll go from there
On the idle screws, close them, clockwise, until they just seat and the open the 1 to 1 1/2 turns each to get started.
I'll assume there is fuel in the tank and the pump is operating since it did before....at least for now
Add fuel through the vent at the top of the carb. You need a really small funnel or be creative. Don't know how much but maybe 1/4 cup or so?
Activate the throttle and see if you get fuel. Maybe the carb is just not getting a prime to it. If you see fuel, try to start and we'll go from there
Safety Car
Joined: Sep 2007
Posts: 4,458
Likes: 331
From: Indy Indiana
no gas to your carb has nothng to do with jet settings, or idle mixture screws.
check to see if you have gas in the line as you crank the engine ( gas hose in a jar as you crank). then see if you have gas in your float bowl ( fuel getting past the filter). check to see if your accelerator pump is working ( gas squirting in the carb as you pump the accelerator). if all this is true then you have gas to your carb. if not, then you have a basic problem long before you need to consider idle mixture and meter and rod sizes.
check to see if you have gas in the line as you crank the engine ( gas hose in a jar as you crank). then see if you have gas in your float bowl ( fuel getting past the filter). check to see if your accelerator pump is working ( gas squirting in the carb as you pump the accelerator). if all this is true then you have gas to your carb. if not, then you have a basic problem long before you need to consider idle mixture and meter and rod sizes.