Off idle stumble or bog.

[Jeff1]

Thank you to all that post and the replys. They have been most helpful.
I'm still tweaking on my 7027211 carb.  I'm trying to adhere to the second recipe.
The carb is really starting to come around. I'm still finding things incorrect from the two previous professionals work. My question today is an off idle stumble and that may be an incorrect description as it really is just prior to the secondary opening.
It's slight but noticeable. I followed some of the bog threads and feel I've covered most of the solutions. I've noticed when first measuring the carb to have a starting point that the accelerator pump discharge holes are at .037 which is a bit larger than the recommendations call for .028 -.030. Could this play a factor ?   One last question . my primary throttle plates were drilled before I acquired it. .063. They are drilled on the side of the plates closest to idle mixture screws. I have no idle bypass air. Does it matter or have any effect what side of the primary shaft the are drilled on ?  Thanks
I can't thank Cliff enough.  Back in my day we didn't have a way to exchange info so easily. This forum and the time Cliff commits to it are invaluable to learning without making all the mistakes we did years ago.

[Cliff Ruggles]

Large discharge holes for the accl pump dump the accl pump charge quickly and early.  Smaller holes will have longer pump shot duration.

If all the pump shot is gone right before the secondaries open it could be the reason for the slight bog.

No mention of what pump is in the carburetor.  We have different duration springs to slow down the pump shot if you are using one of our pumps.  We send them with the strongest spring so it will delivery the fuel quickly and early with huge discharge holes......Cliff

[Jeff1]

Thanks Cliff.  Yes we are using the acc pump you sent. So I assume it's the one wt the strongest spring.  I seem to have cured the bog or stumble by fine tuning of the air door spring tension. A 1/16 of a turn at a time.  An occasional bit of black smoke from the tail pipes at the hit from a rolling start. It's very small and takes some effort to notice. You can't see it from in the car.  Do you see any value in the effort to close up the accelerator pump orfices ( .037) or leave them alone.? One of our crash test dummies ( drivers) has complained or noticed the secondaries not opening. He may be expecting a big hit and I think we are opening them so as not to get that big change.  Any thoughts?  We will keep plugging along fine tuning as we figure it out. Thanks ...Jeff

[Cliff Ruggles]

Primary accl pump shot is important to help get the secondaries on line without bog or hesitation. 

The tension spring for the airflap shaft is a big player and so is the choke pull-off.  The pull-off prevents the flaps from "whipping" open when vacuum falls off when the secondaries throttle plates open.

A well timed pull-off and correctly adjusted linkage to the pull-off can be a big player in hesitation/stumble/bog going quickly to full throttle, especially right off idle or low rpm's.

When you have everything set correctly, transition onto the secondaries should be "seamless".  The engine should rev thru the power range without any noticeable transition, just smooth stead/strong power all the way to the shift point.

IF you feel a big "lunge", or noticeable transition onto the secondaries, it still needs some adjustments......Cliff