Carb a little Rich
Thread Starter
Burning Brakes
Joined: Oct 2006
Posts: 1,044
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From: Henrico VA
Carb a little Rich
My car is running a little rich at idle. I assume it would follow that I am also running rich at speed. I seem to remember at sustained high RPMs (for minutes) I could smell a little gas. Would turning the two idle adjustment screws counterclockwise one turn be a good place to start? Gracias!!!
-Adam
-Adam
Team Owner
Joined: Jan 2006
Posts: 37,637
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From: Crossville TN
Adjusting the idle screws won't cause any significant difference at speed. The power piston inside the carb may be adjusted incorrectly or you may have other adjustments that are not quite right. I would recommend Lars Grimsrud, but I think he is now retired from that work. {And for the Quadrajet crowd, that is a serious loss of knowledge and skill.}
Thread Starter
Burning Brakes
Joined: Oct 2006
Posts: 1,044
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From: Henrico VA
So it's more than just a screw issue? I'm glad I asked. I know that is a huge loss. We hope the best for you Lars.
Adjusting the idle screws won't cause any significant difference at speed. The power piston inside the carb may be adjusted incorrectly or you may have other adjustments that are not quite right. I would recommend Lars Grimsrud, but I think he is now retired from that work. {And for the Quadrajet crowd, that is a serious loss of knowledge and skill.}
Melting Slicks
Joined: Feb 2006
Posts: 3,428
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From: Japan
I would agree with 7T1Vette's inclination- you can easily tinker with the idle mixture screws in the hope of getting it right but you're likely going to find that it's a power piston issue which will require disassembly to correct.
Thread Starter
Burning Brakes
Joined: Oct 2006
Posts: 1,044
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From: Henrico VA
I wired my choke open. I need to make a rod to fit my intake manifold and never got around to it. The car starts great on the coldest VA mornings, but will need some pedal to keep from stalling for a few seconds. I cleaned my air filter not too long ago. I haven't checked my plugs in a while. It could be possible, but I guess I'll look into the power piston explanation.
Team Owner
Joined: Jan 2006
Posts: 37,637
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From: Crossville TN
Just so you don't mis-understand what we are saying....
The idle adjustment screws WILL allow adjustment of fuel mixture for idle condition ONLY. For mixture adjustments in the running range it requires a combination of adjusting the height of the power valve and/or the selection of rod and jet sizes. The carburetor is a device which can allow the approximation of a stable air/fuel ratio across the rpm and load range of the engine. But it is somewhat complex and requires someone with good skills on each specific carb model to 'dial it in' well. Good knowledge, trial-and-error parts exchange, and good experience are needed to do that job well and efficiently. There are books written on how to properly adjust the Q-jet, and if you are interested in digging in that deep, you really should purchase one and read it thoroughly.
The idle adjustment screws WILL allow adjustment of fuel mixture for idle condition ONLY. For mixture adjustments in the running range it requires a combination of adjusting the height of the power valve and/or the selection of rod and jet sizes. The carburetor is a device which can allow the approximation of a stable air/fuel ratio across the rpm and load range of the engine. But it is somewhat complex and requires someone with good skills on each specific carb model to 'dial it in' well. Good knowledge, trial-and-error parts exchange, and good experience are needed to do that job well and efficiently. There are books written on how to properly adjust the Q-jet, and if you are interested in digging in that deep, you really should purchase one and read it thoroughly.
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Thread Starter
Burning Brakes
Joined: Oct 2006
Posts: 1,044
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From: Henrico VA
Understood. Is it easy to adjust the power rod? I've read stuff on the Q-jet before, I just figured I'd see what I could dig up here. rdrnnur has a vacuum gauge and we're going to mess with it this weekend. Do you plug the vacuum gauge into the intake manifold?
Team Owner
Joined: Jan 2006
Posts: 37,637
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From: Crossville TN
Just hook the vacuum gauge to any manifold/carb/vacuum system connection to get a reading. It is best to start this check-out process by removing ALL lines connected to vacuum system and plug them off. THEN connect your vacuum gauge and read it while engine is warmed up and idling. Now re-connect the dist. vacuum advance [along with the vacuum gauge] and take another reading. If you didn't lose vacuum level, then your dist. can is in good shape. Now, you can adjust timing by rotating the dist. to obtain maximum vacuum reading. Next, adjust carb idle settings and idle speed to your satisfaction. Now read vacuum level again; that value establishes your 'baseline' vacuum reading...the value to compare any further readings with for finding/fixing vacuum leaks in the system. Reconnect your other vacuum system lines and take another vacuum reading. If the vacuum level didn't drop more than 1" Hg [or so], you don't have any significant vacuum leaks in the headlight/wiper/HVAC systems and you should be "good to go". If the level does drop a lot, it is time to search for leaks in the vacuum systems (I won't go into that here). Have fun! 
