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Jet size and power valve vacuum rating will not affect your idle as
long as you have the throttle plates adjusted where they should be.
Your main circuit is not being used at idle.
Do your idle mixture control screws have any affect on how the car idles?
From: Who says "Nothing is impossible" ? I've been doing nothing for years.
Originally Posted by TheSkunkWorks
Good points by DRIVESHAFT there.
And, not to be forgotten is one of my favorite Lars'isms, that ~90% of all carb problems are ignition problems...
Yes the point about the idle mixture screws is the key. If they have no affect on the idle then the idle feed restrictors are too big. If they are too big you are going to have a rich idle and cruise. This is why the Mighty Demon is such a good carb. They have screw in IFR's and all you do is screw in smaller ones until you get the adjustment back.
This post reminds me of posts in past when someone would post how great Barry Grant carbs were because his motor ran like crap with 20 year old, gummed up Holley on it. So he changed it to a brand new BG carb and now his motor ran great. So now Holley carbs were crap and BG carbs were the cat azz.