how to get a lean idle on the Q jet

[turtlevette]

Are we discussing my car or which AF monitor to get.?

Why does every single question on this forum get muddled?

Looking at my carb it appears the throttle butterflies are worn out. The primarys don't shut completely with spring tension. Or they do shut completely and forcing it more by hand moves the shaft in the bore. I can't tell.

I thought QJs did have idle air bleed slots in the venturi though. The primaries have been adjusted completely closed as long as i can remember.

I would think the idle would be very inconsistant if it were a vacuum leak or poorly returning butterflies.

 

[lars]

If the primary throttles are fully closed and the carb still idles it means you have an air leak. You should be able to kill the engine by closing the idle speed screw. If not, there is a vacuum leak problem or a carb problem.

There are no idle air bleed slots in the venturi. There are idle air bypass holes in the throttle plate bores below the throttle plates, and there are idle fuel transition slots in the throttle bores above and below the throttle plates. In the venturi area, there are low speed and high speed air bleeds, but these are fixed with no adjustment possible (other than drilling), and they are holes - not slots.

A steady vacuum leak can produce a stable idle speed. If your idle speed screw is fully backed out and you're forced to set idle speed through mixture adjustment, you have problems that need to be solved - you cannot tune the carb properly with a vacuum leak allowing the engine to idle with the throttles closed.

Lars

 

[turtlevette]

If the primary throttles are fully closed and the carb still idles it means you have an air leak. You should be able to kill the engine by closing the idle speed screw. If not, there is a vacuum leak problem or a carb problem.

There are no idle air bleed slots in the venturi. There are idle air bypass holes in the throttle plate bores below the throttle plates, and there are idle fuel transition slots in the throttle bores above and below the throttle plates. In the venturi area, there are low speed and high speed air bleeds, but these are fixed with no adjustment possible (other than drilling), and they are holes - not slots.

A steady vacuum leak can produce a stable idle speed. If your idle speed screw is fully backed out and you're forced to set idle speed through mixture adjustment, you have problems that need to be solved - you cannot tune the carb properly with a vacuum leak allowing the engine to idle with the throttles closed.

Lars

Ok, i'll spray some penetrating oil around and see if the idle changes. Its probably leaking through the well worn throttle shaft penetrations.

 

[lars]

Worn throttle shafts won't in and of themselves cause a vacuum leak of any significance. Rather, excessively work throttle shafts can cause the throttle plates to "cock" in the throttle bores and fail to fully close. If this is the case, you can relocate your throttle return spring from the bottom of the throttle lever to the top of the throttle lever and have the spring pull forward instead of back. This will equalize the force on the shaft beween the throttle cable and the return spring, and the throttle will fully close even with a worn shaft.

If you need new shaft bushings, I can install them for you and test run the carb to verify it.

Lars

 

[turtlevette]

Worn throttle shafts won't in and of themselves cause a vacuum leak of any significance. Rather, excessively work throttle shafts can cause the throttle plates to "cock" in the throttle bores and fail to fully close. If this is the case, you can relocate your throttle return spring from the bottom of the throttle lever to the top of the throttle lever and have the spring pull forward instead of back. This will equalize the force on the shaft beween the throttle cable and the return spring, and the throttle will fully close even with a worn shaft.

If you need new shaft bushings, I can install them for you and test run the carb to verify it.

Lars

I'm honored that you would offer to work on my carb but i drive the car everyday. I was thinking i'd eventually replace the baseplate with a parts QJ from an 83 suburban a friend gave me. It has the proper attachment point for the 700r4 TV cable.

i backed out on the mixure screws and it's less stinky for now.