With a typical Holley, restricting the main air bleeds typically will delay the mains starting. It also doesn’t take big changes on the bleeds to make big differences. A .010” wire is a big jump and should shift the mains starting higher in rpm. I’ve spent a lot of time at racing fuel systems website reading to get my Holley where I want it. Here’s a graph I found that really has helped me understand what’s doing what and when.
Also stumbling at low throttle while in the transfer slot very well could be not having enough transfer slot exposure. My thought there is the transition circuit may not have flow established and that has to occur before feeding mixture to the engine causing an off idle stumble.
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