O320 Carb Problem

Have an older RV-4 with unfiltered ram air set up. Has a step or stutter as you advance RPM. Slow throttle advance stutter is passing through 1200 RPM, Fast throttle advance stutter is at 900 RPM. Original carb was just replaced with a rebuilt by my local IA and I. It had leakage issues. Both Carbs have had this stutter during throttle advance. The new carb is a bit better, but still has the stutter. IA and I have checked for induction and exhaust leaks. All seems fine. Has any one else noticed this with the unfiltered ram air set up?

If you have a primer, try disconnecting it and capping the engine fitting off. I would also try setting the idle mixture way lean or way rich and see if that helps. Also you might try re-rigging the accelerator pump linkage to change the schedule of how it dumps fuel into the carb. If you look at the throttle shaft you will see that there a re a few holes you can move the linkage too, to change the way the pump discharges relative to the throttle movement.
Good Luck,
Mahlon
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