Hot Rod Forum : Hotrodders Bulletin Board - View Single Post - Initial timing
Thread: Initial timing
View Single Post
  #24 (permalink)  
Old 02-20-2013, 09:30 PM
F-BIRD'88's Avatar
F-BIRD'88 F-BIRD'88 is offline
Yada Yada Yada
Last photo:
Join Date: Oct 2005
Location: Ontario, Canada
Posts: 9,197
Wiki Edits: 0

Thanks: 5
Thanked 386 Times in 380 Posts
I suggest you go back to the 70 idle air bleeds. The wide band will show you what it really wants for a pri idle air bleed. You can make your own by soldering up and redrilling with a .062" drill bit (1/16").
Then as that will likely be a bit too rich as shown on the AFR gauge (off idle, transition) you then fine tune the size by hand a little at a time using the drill bit as a hand hone in the air bleed, till its just right.

You tune the off idle with the AFR gauge.. not the curb idle. The curb idle is set according to the manifold vacuum gauge and best idle quality (it will be between 12.5 and 14:1 at idle)

The off idle must not shift too far lean or rich as your open the throttle. +/-14.7 is good.

Then watch the gauge as you open the throttle further and the primary main jet flows fuel.
takes a bit to find the best balance and a good transition.

Very small changes make a big difference. a .004" change is a lot.
By custom hand sizing the soldered up air bleed by hand you get it much more exact than buying different bleeds.

any all air leaks will throw off the AFR gauge, including header gasket leaks.

You must always test the final size of the air bleeds with the air cleaner installed. Ya it matters.
That's how sensitive they are.

You can shift the AFR of the idle circuit by hand with fingers partically over/restricting the idle air bleeds and watch the effect on the AFR gauge
while the engine is running at idle and off idle. (when you open the throttle a bit from idle)

I bet you will end up with a custom pri air bleed size between .065" and .070" The afr gauge shows you the way.

Last edited by F-BIRD'88; 02-20-2013 at 09:39 PM.
Reply With Quote