I bet you a pound to a pinch of sh!te it`s just your carbs need balancing.
You do it by adjusting the spring loaded screw between the carbs on the throttle linkage. You need to synchronise, or balance the throttle slides so they open simultaniously.
I had the same issue long ago.
It`s a bit of a pain if you have the stock airbox fitted, is also easier to do with the tank removed and an auxillary tank fitted temporarily. You can extend the fuel line from the standard tank and sit it on the bench as an alternative.
I got fed up trying to synch the slides by eye and did it by ear and eye instead in the end. Whatever works for you.
Once they`re set you should be able to adjust the tickover quite easily and have both exhausts getting warm on idle.