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Thanks guys, I forget where the screws are Steve, to be exact.
I have had the mixtures spot on most of the time as far as popping goes however they are out of adjustment at the moment.
It's mainly when fleeing from sports bikes that I think of adjusting mixture, just when I don't have a tank bag with a screwdriver.
It isn't difficult to organise a screwdriver but the amount of times (over 18 years) that I've thought 'geez it would be handy if I could adjust them now (easily on the side of the road before the sporties catch up )......

George, re the air leaks, carbs to heads are good as are exhaust nuts.
There is however a leak at the left hand side of the forward balance pipe.
That would account for the occasional blustering whoosh of a backfire under serious engine braking!
Point well taken about sorting that leak.

Dougie, adjusting the left mixture screw with my right hand and vice versa would be difficult.
Difficult, but do-able I think. (with my knurled extended mixture screws!)

Sometimes I think there might also be an air leak between my ears, but I'm stuck with that one.

I moved mine out a tad before going to work (at about one full turn out now), and put a screwdriver in the tank bag. 25 minute ride, thru countryside and freeway, then suburbs to work. Idle at a little over 1200rpm, so tweaked the idle a little less.

The popping is now just a slight burble, but I haven't done any heavy engine braking just yet to encourage loud popping. Maybe tomorrow on the way to work.

My inlet stub at the left cylinder was loose, and tightening that helped a lot, but wasn't the whole answer.