Shell game mystery… another hanging idle riddle

I hate to start another runaway or hanging idle post but I stumbled on to something today that makes no sense to me. All set up with an hanging gas line, propane line, bright lights and patience to find what I’m sort of hoping is only an air leak. Also, got my carbs back from one of the kings of church of clean carbs… Rick from Oldskool Carbs in South Carolina.
here’s the ODD part; if I leave the golf tee out of the petcock tube it idles fine. If I take of the cap to the boot hookups ( for my mercury motion pro) it idles fine. EXCEPT if I take of the cap on carb one ( the clutch side most outer) then it makes no difference. let me restate this; if I completely remove the rubber cap from any intake on #2,3 or 4 it idles great and the moment I put the cap back on it revs up to eventually 4,000.
what am experiencing here?

 

Are the carbs sync'd via a running sync?

 

We have to assume Oldskool Rick knows his stuff, so that assumption includes replacing all the rubber bits and cleaning the vital passages.
An invoice of $400+ is probably in-line for all this.
Now, start by closing each mixture screw and opening them 2-1/2 turns. Rick rebuilt them, he isn't tuning your bike, this is your job.

Exactly, without this step you're chasing your tail.
Also have you verified your valves are in tolerance?
Ignoring the valves for the moment, you probably have things close.
When you had all the caps in place and your idle rose to 4,000, did you try turning the idle down?

 

Sorry I just re-read your reference to your "mercury motion pro" so you have a sync gauge set up.
With the petcock on "pri" and the gauge plugged into all 4 nipples there's no need to unplug any hoses until its idling correctly.