Jet - Rod Question - Lars?
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Racer
Joined: Apr 2001
Posts: 395
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From: Shoreline WA
Jet - Rod Question - Lars?
On my NOM 71 vette I have a Edelbrock #1901 Q-Jet Carb. According to the Edelbrock website this carb has the following jets and rods installed:
Main Jet: .069; Metering Rods: Primary-36B, Secondary-DR
The calculated metering areas from this combination are:
0.00272 Meter Area @ Cruise
0.00321 Meter Area @ WOT
According to Lar's Quadrajet Paper, the original 7041212 carb had the following jets and rods installed:
Main Jet: .074; Metering Rods: Primary-44, Secondary-AR
The calculated metering areas from this combination are:
0.00278 Meter Area @ Cruise
0.00377 Meter Area @ WOT
As you can see the Edelbrock is setup a little leaner than the original Quadrajet.
With an Engine suffix code of TMM, the engine is either a:
1980 350 170HP or a 1974 350 145HP
The only visible performance change has been the addition of a Perfomer manifold. I do not know if the cam has been changed.
Should I use the existing Edelborck jets and rods as a starting point or replace them with the ones used in the 7041212 carb and begin tuning from there?
Mike
Main Jet: .069; Metering Rods: Primary-36B, Secondary-DR
The calculated metering areas from this combination are:
0.00272 Meter Area @ Cruise
0.00321 Meter Area @ WOT
According to Lar's Quadrajet Paper, the original 7041212 carb had the following jets and rods installed:
Main Jet: .074; Metering Rods: Primary-44, Secondary-AR
The calculated metering areas from this combination are:
0.00278 Meter Area @ Cruise
0.00377 Meter Area @ WOT
As you can see the Edelbrock is setup a little leaner than the original Quadrajet.
With an Engine suffix code of TMM, the engine is either a:
1980 350 170HP or a 1974 350 145HP
The only visible performance change has been the addition of a Perfomer manifold. I do not know if the cam has been changed.
Should I use the existing Edelborck jets and rods as a starting point or replace them with the ones used in the 7041212 carb and begin tuning from there?
Mike
Tech Contributor
Joined: Aug 1999
Posts: 14,380
Likes: 6,391
From: At my Bar drinking and wrenching in Lafayette Colorado
Re: Jet - Rod Question - Lars? (SLine78)
Mike -
Take the car for a cruise and then yank a spark plug and do a plug reading. If you're running pure white, swap the jetting over to a 74/43 combo. This will give you a bit more snap if you're on the lean side. The 69/36 combination is the jetting combo for a truck. It works well for most passenger car applications, but may be a touch lean for your setup. But check the plugs first: If you're runing tan, you're okay. If you're closer to white, jet it up. And don't forget to set and verify that you're running your total mechanical timing at 36 degrees - don't try tuning the carb until you have that total timing set and checked.
Take the car for a cruise and then yank a spark plug and do a plug reading. If you're running pure white, swap the jetting over to a 74/43 combo. This will give you a bit more snap if you're on the lean side. The 69/36 combination is the jetting combo for a truck. It works well for most passenger car applications, but may be a touch lean for your setup. But check the plugs first: If you're runing tan, you're okay. If you're closer to white, jet it up. And don't forget to set and verify that you're running your total mechanical timing at 36 degrees - don't try tuning the carb until you have that total timing set and checked.
