Carburetor idle air bleeds

astikhossw · 10-23-2013, 11:48 AM

Do any of you guy's know if the idle air bleeds on the secondary side perform a bleed function on a vacuum secondary carb.,The reason that i need to know is that i am going try out my QF 780 carb. next week and it is idling to the point of stalling (lean)and i had no control of the idle mixture screws,so i notice that the air bleeds on the secondary side were smaller than the primary side so i swapped them over and now i have some control of the mixture screws and it idles alot better without stalling.

Tom Goldman · 10-23-2013, 11:09 PM

The secondary idle circuit pulls a small amount of fuel at idle but nowhere near the amount of the primaries.
I would call Quickfuel's tech dept. ,they are really good guys to deal with , and see if they recommend going larger on the primary idle feed restriction to allow more fuel in the idle circuit ,along with the smaller air bleeds.
You may need more fuel than just going smaller on the air bleeds can provide, especially on the off idle transition to full throttle.

astikhossw · 10-24-2013, 11:32 AM

Thanks Tom,I'll do just that.

jmarkaudio · 10-24-2013, 06:28 PM

If it's a 4 corner idle carb the idle circuits should be mirrored including bleeds. If the secondary has a metering plate or is a 2 corner idle it won't. The SSR 780's I had through my hands were 4 corner idle.

Tom Goldman · 10-25-2013, 01:01 AM

If its the approved S/SS NHRA replacement carb , I believe it can only have the primary idle circuit adjustable , and has a non adjustable secondary idle circuit .
Not 100% sure on that , but pretty certain.

jmarkaudio · 10-26-2013, 05:45 PM

As delivered the secondary is adjustable with short mixture screws, they must be plugged once in competition. They supply lead plugs, much like the emission carbs had the idle screws plugged off. Not real sure why, it offers no real advantage having 4 corner idle.

10-23-2013, 11:48 AM	#1
astikhossw Member Join Date: Jul 2008 Location: moreno valley Ca Posts: 266 Likes: 2 Liked 20 Times in 9 Posts	Carburetor idle air bleeds Do any of you guy's know if the idle air bleeds on the secondary side perform a bleed function on a vacuum secondary carb.,The reason that i need to know is that i am going try out my QF 780 carb. next week and it is idling to the point of stalling (lean)and i had no control of the idle mixture screws,so i notice that the air bleeds on the secondary side were smaller than the primary side so i swapped them over and now i have some control of the mixture screws and it idles alot better without stalling.

10-23-2013, 11:09 PM	#2
Tom Goldman VIP Member Join Date: Jan 2003 Location: Allentown,PA Posts: 2,477 Likes: 892 Liked 883 Times in 237 Posts	Re: Carburetor idle air bleeds The secondary idle circuit pulls a small amount of fuel at idle but nowhere near the amount of the primaries. I would call Quickfuel's tech dept. ,they are really good guys to deal with , and see if they recommend going larger on the primary idle feed restriction to allow more fuel in the idle circuit ,along with the smaller air bleeds. You may need more fuel than just going smaller on the air bleeds can provide, especially on the off idle transition to full throttle. __________________ Tom Goldman 1500 SG , 1506 STK

10-24-2013, 11:32 AM	#3
astikhossw Member Join Date: Jul 2008 Location: moreno valley Ca Posts: 266 Likes: 2 Liked 20 Times in 9 Posts	Re: Carburetor idle air bleeds Thanks Tom,I'll do just that.

10-24-2013, 06:28 PM	#4
jmarkaudio Junior Member Join Date: Apr 2008 Posts: 83 Likes: 0 Liked 0 Times in 0 Posts	Re: Carburetor idle air bleeds If it's a 4 corner idle carb the idle circuits should be mirrored including bleeds. If the secondary has a metering plate or is a 2 corner idle it won't. The SSR 780's I had through my hands were 4 corner idle.

10-25-2013, 01:01 AM	#5
Tom Goldman VIP Member Join Date: Jan 2003 Location: Allentown,PA Posts: 2,477 Likes: 892 Liked 883 Times in 237 Posts	Re: Carburetor idle air bleeds If its the approved S/SS NHRA replacement carb , I believe it can only have the primary idle circuit adjustable , and has a non adjustable secondary idle circuit . Not 100% sure on that , but pretty certain. __________________ Tom Goldman 1500 SG , 1506 STK

10-26-2013, 05:45 PM	#6
jmarkaudio Junior Member Join Date: Apr 2008 Posts: 83 Likes: 0 Liked 0 Times in 0 Posts	Re: Carburetor idle air bleeds As delivered the secondary is adjustable with short mixture screws, they must be plugged once in competition. They supply lead plugs, much like the emission carbs had the idle screws plugged off. Not real sure why, it offers no real advantage having 4 corner idle.