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Originally Posted by Mike Braddock
Guys,
I have a question about the carb we're currently running on our engine. It's a mild 351C with a dual plane intake, 9.4:1 compression and a very mild cam (6k RPM max). A friend gave us a 4150 700 cfm double pumper that we thought would work pretty well. We're having trouble leaning out the idle mixture. Does anyone have enough experience to tell us whether this is just too much carb for this mild of a motor? I know I'm not running on the transition circuit, as I had to drill .1" holes in the primary throttle plates to allow me to close the butterflies enough to not expose the transition slots at idle. Do the main jets have any affect on idle? I thought the idle feed restrictions, idle air bleeds and the idle mixture screws were the only things that affected the idle but I wanted to ask someone with more experience. The carb is newly rebuilt and appears to be working properly with the exception of my idle tuning. The idle mixture screws are about 5/8 of a turn off their seats, which tells me something else is wrong from what I've read. Thanks guys!
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Mike, what tells you to lean out the idle mixture?
What vacuum reading are you getting at idle?
What power valve are you using?
You state a "very mild cam" What is the duration at .050, overlap, and lobe centerline? With a very mild cam and mild 6K Cleveland you should not have to drill air holes in the primary butterflies for idle quality.