My experience with a y-piece
My bike runs like a dream.
But it is modified in many respects, I'll elaborate.
I have a little opened up air box, with K&N free flowing element. The carbes were renewed - all jets, needles' diaphragm etc replaced. leading edge of carb slide smoothed. all intake junctions smoothed.
Intake and exhaust ports were lightly ported - no change in section or gas flowd, just smoothed to the max.
Original pipes, a German made Y-piece, a modified Laser end can - more opened up.
1000cc Siebenrock kit.
The carb tune was changed from standard - needles are higher up than standard, dont recall how much.
I changed to the Y-piece when my collector box rotted out. When I mounted it, I couldn't use full throttle as it was detonating like mad. I put in bigger mains and the bike ran like a mad dog.
I is lowder than standard BMW, no doupt. But not to the point it makes my neighbors angry. I ride with ear plugs regardless.
One more important thing - Alibaba metioned also - you must start with comletely new jets and needles before any conclutions. Needles in particular, tend to erode, together with their respective jets, exactly where they work most of the time - midrange. The vibrations causes it. Mine had, when I bought the bike, a dancer's waistline.
Miky