Guys ,
Bog standard MC21 which starts and runs really well but noticed today that the 2 exhausts have quite different characteristics.

Today on a paddock stand at tickover, the right hand lower cylinder exhaust runs warm , popping nicely with quite a bit of back pressure just how I would expect one of my old single cylinder motocross bikes to run .

The left hand upper cylinder one runs really cool , even at full running tempereture , doesn't seem to make hardly any noise or back pressure and smokes slightly more , but things even out instantly with a few revs.

Is this normal for an NSR or is it a case of ' There may be trouble ahead' ?

Thanks in advance

have you done a compression check on both cylinders?

Yes both cylinder compressions are spot on . The spark is also good so its obviously a fuel thing .
I'll investigate today . Thanks

First thing I always do with this scenario is swap the plugs.

It`s just the throttle slides that need balancing.
Not too hard a job.
There`s a spring loaded adjustment screw in the middle of the throttle linkage at the top of the carbs.
Need to take the tank off to access it if you`ve got the standard airbox fitted. Will have to rig up a little fuel tank.
When the bikes idling, just tweak the screw 1/8 to 1/4 turn at a time and see how the bike reacts.
Should be easy to achieve a good balanced idle from both cylinders.

You can just do them by eye, on the '28 unless you have weeks to spare it's the only way (carbs off and apart to get at the balance screw).
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I set them up by eye first.
Generally I find it`s always a bit out after starting the bike up.
I find it`s much easier to have the bike running.
Once it`s up to temperature, I find it`s very easy to balance the carbs.
After each tweak of the adjuster screw, let the engine settle. Then give it a couple of rev-ups & let the throttle go to settle the linkage.

Thanks for the advice . I'll give that a try .