No blockage in the nipple. All parts move when I turn the screw. Could an imperfection with the butterfly valve, a scratch or nick cause something like this?
That's very doubtful!
It's been some time since I last synchronized mine but I remember the same difficulty on the left bank and it's definitely related to the way those carburetors are hooked to each other by way of the linkage.
A close look at that singular area will reveal what I mean. If you adjust the screw for #2 then the result will be an adjustment to #2 only, but the other screw will adjust #4 and change the adjustment for #2 at the same time!
Like I previously stated, the most important thing is to keep the idle speed constant . The recommendation I seem to remember is to use a more sensitive tachometer than the one that is on the bike. Obviously this makes better sense with the emphasis being on idle rpm maintenance while making adjustments.
I feel this point (maintaining a uniform idle speed) is not given the importance it deserves thereby affecting the completeness of the synchronizing experience.
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