A few years ago I fitted a set of New 350 carbs to my GTR and they nade a whole world of difference. On the old carbs the bike wouild not run cleanly on light throttle, such as when cruising through town or in traffic, and would only do about 41 miles to a (UK) gallon. I'd had the old carbs cleaned and blown through as well as I could, and had the float pivots re-bushed, but it made no difference to teh low speed running. With the new carbs, the problem cleared completely, and I found I was getting around 45 miles to a gallon. I guess that after 30 or so years, the pilot air passages must have become partially blocked, but it was a well worth while change.
The only thing I would check is hat size jets you have. The 350s all left the factory with #140 main jets (slightly rich to help cooling during initial break-in), and these should (??!!) have been changed for #130 jets at the first service. It is quite possible that New spare carbs also left the factory with #140 jets, and the motor will definitely runs too rich on these. Maybe you'll find a pair of #130s in your old carbs, but if not, I'm sure Richard will have some somewhere!
Graham
