[Roadsters] High Speed Hesitation / Potential Fix?

[wattaj]

I have been chasing this issue for a while and I am hoping I may have found something but would like your feedback.  (Thanks in advance!)
When cruising around 3000 to 3200 RPM, if I press on the accelerator, the motor wants to hesitate or cough, it will eventually get beyond this, but is annoying.  I have done my best to tune things and the only thing that helps is making the front carb run very rich.
Today, when dissembling the carbs, I noticed the front carb was missing the Lifter Piston (part # 16324-10400) that you can use to test the lean/rich mixture from the bottom of the carb without having to put your finger into the throat of the carb.  
Could that be creating a vacuum leak and cause of my issue?
Thanks,Alan
67-1600 (with a 67.5 engine)Portland, OR
  
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