Dual Quad 428 CJ

[Khobra]

Originally Posted by DanEC

Jerry's advise is generally the text book guide to selecting power valves. Not sure what happens if a lower range one is used than needed - possibly a rich condition.

Are you carbs sensitive to idle mixture adjustments and the primary throttle blades resting around the middle area of the little idle transition slots in the bores? Or are they resting at the top of the slots at idle?

And I assume you are tuning the idle mixture and speed on both carbs equally?

Normally I would think you are just fighting the characteristics of a fairly big cam if those duration figures are at .050 inches lift, but if you can pull 12 inches of vacuum at idle I think you should be able to get an outcome that isn't obviously rich. But even my 231/236 @ .050 cam with my dual quads is not something I let idle inside my garage for long.

Dan and Undy,
Thanks for your input. Yes, idle mixture screws are somewhat sensitive but not like they should be. The throttle plates are nearly closed and yes, both carbs adjusted equally. Spoke with a very knowledgeable individual at the race track today and I think he is on the right track. I need to increase the size of the idle air bleed restrictions. This will be my next step. I will drill out the current restriction and tap and install a screw in type.

Undy, did you have to play with this on your carbs?

My linkages are bang on, the power valves are 6.5. In the past, on other applications, I have drilled small holes in the primary throttle plates which did help a huge amount but I don't want to go that direction in this case if I don't have to. I would rather take the air bleed restriction route.
Hopefully I can do this sometime this coming week.
Will keep you posted.
BTW undy, what is your initial and total advance that you're running on your engine? I'm at 16 initial and 36 deg. total.