Involuntary Street Twin At Idle/low Rpm

Hello, new member hoping to find some help here!

I recently got my first Triumph (after spending over a decade dreaming of having one) in a 2011 street triple, but sadly it seems to have come with some problems the dealer failed to catch/mention.

At idle and low rpm (under 4000) it seems one of the cylinders is only coming to life intermittently, and will only kick in once the revs have climbed up a bit.
This makes riding at low speeds pretty uncomfortable obviously, has also resulted in some unpleasant clacking noises and juddering when trying to accelerate from low rpm, and fairly frequent stalls at idle with clutch in.

I thought it might just need to be ridden a bit after having probably been stood for a while, or fresh fuel, but neither of those has seemed to help. Am reluctant to ride it much more without fixing if possible. Spark plug or fueling problems also seemed likely but it looks like a bit of a mission to get at them so thought I would check if anyone had any advice before I start taking things to pieces.

Might be worth mentioning that it seems the bike has been dropped at some point on its right hand side, but with minimal visible damage, slightly bent foot-peg, cracked indicator.. etc.

That aside seems in very good condition and runs like anything once the revs are high enough.

Would be very grateful for any insight or advice at all!

I will add some videos to show the problem too.

 

Thank you!

Yeah I am a bit annoyed with the dealer really, to put it lightly. However, I am not sure if they are even competent enough to do anything about it.
There was nothing to suggest it had any problems in the listing, except perhaps a vague "good bike for people who can maintain themselves". Should perhaps clarify that this is in Japan..
Just a general used vehicles dealer not a triumph specific one and the bike was delivered from across the country so taking it back could also be a bit of an ordeal. Will see what can be done though.

There is also a triumph dealership a little closer to me too so might be worth taking it there!

 

Just a quick update in case anyone has a similar problem, turns out it was just the spark plug on he right hand side that needed changing, as suspected! Running perfectly now thankfully.

Thank you all for the advice and quick responses here!