Secondary Butterflies fully shut at idle?
05-20-2011, 07:15 AM
#1
Secondary Butterflies fully shut at idle? Have one more carb issue I’m seeking advice about. .
When I originally set up the carb (Holley 750 DP with mechanical secondaries, LS2 6.0L) I adjusted the primary blades opening such that 20 thousands of the transfer slot was showing (little square dots on both primaries). I then used the secondary idle setting to set the idle speed. Ran good like this, was able to get the idle at ~800 RPM with wideband showing 14.7, all four idle screws a little over ¼ turn out.
Carb was having some problems with the throttle sticking on a high idle when hot. So to try and fix this I pulled the baseplates off and cleaned everything up to free the motion. When I did this I noticed the secondary blades were fully shut. When I put everything back together I set the initial primary and secondary blade openings such that 20 thousands of the transfers slots were showing both front and back.
With the carb like this I had to open the idle screws to about one full turn open to get the AFR back to 14.7. Car was idling at about 1800 RPM like this. I then backed off on the secondary idle adjustment to restore the idle. This required putting the idle screws back to ¼ turn to restore the AFR at idle.
So what do you guys think, is this a problem? I haven’t looked but I imagine the secondary blades are fully shut again. Should I just forget about it, or is there something I should be doing different?
I’m running a stock LS2 cam and pulling 23 inches of vacuum at idle. Maybe I just need a bigger cam
??
When I originally set up the carb (Holley 750 DP with mechanical secondaries, LS2 6.0L) I adjusted the primary blades opening such that 20 thousands of the transfer slot was showing (little square dots on both primaries). I then used the secondary idle setting to set the idle speed. Ran good like this, was able to get the idle at ~800 RPM with wideband showing 14.7, all four idle screws a little over ¼ turn out.
Carb was having some problems with the throttle sticking on a high idle when hot. So to try and fix this I pulled the baseplates off and cleaned everything up to free the motion. When I did this I noticed the secondary blades were fully shut. When I put everything back together I set the initial primary and secondary blade openings such that 20 thousands of the transfers slots were showing both front and back.
With the carb like this I had to open the idle screws to about one full turn open to get the AFR back to 14.7. Car was idling at about 1800 RPM like this. I then backed off on the secondary idle adjustment to restore the idle. This required putting the idle screws back to ¼ turn to restore the AFR at idle.
So what do you guys think, is this a problem? I haven’t looked but I imagine the secondary blades are fully shut again. Should I just forget about it, or is there something I should be doing different?
I’m running a stock LS2 cam and pulling 23 inches of vacuum at idle. Maybe I just need a bigger cam
?? 
05-20-2011, 08:18 AM
#2
Teching In
Join Date: Sep 2007
Posts: 16
Likes: 0
Received 0 Likes
on
0 Posts
If you have no other vac leaks, you may need to turn the idle curcuit screws out further to achieve your desired secondary throttle plate position. i.e. 1 1/2 turns seems to be the norm on my dominator...
