Just to throw my 2 pence in;
My '28 was rebuilt recently and running an open airbox (i.e. no lid and some wire holding the filter in place). After Stephen had a little play with the needle it was fine, would take a wide open throttle right from just about tickover to the red line and gave 60.7bhp. Slightly less clean mid throttle but still OK. Real loud induction roar too, probably just like your after.
But on the same day I saw Steve's '18 drop about 2/3rds of a bhp (not much I know, but a drop) and lose throughout the rev range by having another 2 holes put in the airbox lid, thus we can conclude that Steve's setup benefits from some level of restriction on the airflow, so maybe mine would too? Time constraints on the day meant I never got to try it so I did this afternoon, the lid I had lying around already had 2 little holes in which I enlarged to about 1" each before fitting.
What a difference, a bit better at full throttle but part throttle is just transformed, you can potter around town with tiny throttle openings and 3000 or so revs perfectly (just as Honda intended I suppose, I've never run it on normal jets, pipes, card etc.).
Add to that the fact it's now quiet enough to do quiet trackdays and not annoy monkey's neighbours too much when if I leave his place late (or the police) and I fail to see the drawback.
Obviously I plug chopped it (I pulled in the same place as I seized it last time) and it's still running a bit on the rich side so thats nice.
I'm not saying it'll work for you as I also saw Andy's bike make more power with no filters than with the pods, I'm just saying you've got to try for yourself.
Also any mod to make a better sound is a bit dodgy in my book, surely you modify to improve the perfromance and that in turn makes it sound right?
But putting the lid back on has made my bike sound a bit like a scooter
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