I have the same problem but it's the rear cylinder that's running cold.
Also if you feel the exhaust from both pipes by placing your hand close to the exhaust cans, the pulse is much stronger from the front cylinder that the rear at idle.
The left exhaust(rear cylinder) has cold exhaust and a much lower pulse, it also sound like it stutters every 9-10 seconds and the returns to normal.
Can you check this on your bike an post results.
The mechanic said he balanced and cleaned the carbs and checked the coils and plugs. All were OK.
He noticed it too and tried to even them out but when he got close the bike ran very badly so he set the carbs back to standard as per manual.
I posted on this some time back but I can't find a satisfactory answer to it.
I don't expect it's normal as I would expect both cylinders to run at even temperature.
There's something not right some where but I can't find where or what could be causing the problem.