Carb (NOT jetting) question - new!

4 replies to this topic
  • Bibleman

Posted September 03, 2007 - 03:55 PM


Does anyone know what is under the small round cover with the hose on it and two screws on the "L" carb? It's near and to the rear of where the throttle cable bracket is on the right side. I had mine blocked off, but I'm told it should be connected to a nipple in the front of the carb. Supposedly there's a diaphram in there. What's in there, what does it do and what would be the symptoms of a malfunction????

  • Ryanthegreat1

Posted September 03, 2007 - 05:30 PM


That would be the air cut off valve and it does have a diaphragm and associated spring. The nipple for the valve should be connected to the nipple on the front of the carb (nearest to engine on the top) and if you still have the smog pump it would be connected to that as well.

As for symptoms... If the nipple on the front of the carb is open to atmosphere I would imagine it would cause a very lean condition as its a huge vacuum leak.

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  • Ryanthegreat1

Posted September 03, 2007 - 05:43 PM


Ok after pulling this carb on my desk apart I really have no clue as to what that valve does other than control he flow of air.

From what I can tell the valves action is controlled via vacuum and under heavy vacuum the valve is in an open state, such as at idle and decel. Opening the valve opens a path for air from the underside of the CV slide's diaphragm to the float bowl.

And that is as much as I know. If someone could chime in on which direction the air is flowing through this valve and how it affects things please help!

In the mean time its off to learn just how these constant velocity carbs do their magic.

  • Ryanthegreat1

Posted September 03, 2007 - 06:05 PM


I found it! The air cut off valve serves to richen the air fuel mixture when the throttle is closed. Without the valve working the mixture goes lean on closed throttle causing the exhaust popping under deceleration.
About the middle of the page has the info.

  • Bibleman

Posted September 03, 2007 - 07:07 PM


OK, all this would make perfect sense because I had everything blocked off and was still getting a little deceleration popping. I just connected the two aforementioned outlets and will see if it makes a difference. Thanks for the info guys!

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