Most cages have hydraulic lifters. Some bikes do as well, including the Vulcan 1500/1600. They are self-adjusting.
As engines age, the valves recede into the seats in the head. Another problem that is relatively uncommon is the valve stem will stretch (and it WILL fail if this is happening... but regular checks will reveal one valve closing tolerances faster than the rest and give you a clue to a potential problem).
As the valves recede, this closes the clearance, until eventually the valve does not completely close. This results in the valve not sealing, resulting in backfire through either the intake or exhaust, loss of power, and burned valves. This is particularly bad for exhaust valves. This valve has the hot exhaust passing it when it is open, and it is cooled ONLY by it's contact with the seat and head. It is rare for an intake valve to burn, but it can happen.
The US spec for the 900 is to check the valves every 15,000 miles. The AUS spec is every 26,000 miles. Different bikes are different... my 1981 CB750 specs a check every 7,000... at 12,000, two are toward the bottom of tolerance but are okay for another 7,000 or more.
Signs that it needs an adjustment?
It's too quiet.
Seriously... by the time you are showing symptoms, you are far beyond the need for a "check" and are potentially already looking at the need for a valve job.
2006 1600 Ultra-Classic
Patriot Guard Rider
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