Hope the rain stopped. It's beautiful by me and I'm out the door soon to ride!
I'm not a slide expert by any means, but Scottie said it. By shaving the bottom our our BS29 slide, we reduce the size of the cutout thereby richening things up. The combo between slide and needle really effect that 1/8 to 1/4 throttle response I believe.
I always get by terms mixed up on the needle notches. Scottie's explanation is what I meant to say, but he's done a much better job.
Answering both you & Scottie:
Couldn't get back to you before this. The twin granddaughters (12yo) stopped by.
I see what you're saying now about increasing the cutout area on the slide. Hope I don't have to go there. Or drilling out the two holes in the bottom.
Here's what I did before the girls arrived:
I pulled the carb & raised the needle 1 shim (.002") or 1/2 a notch. I set the mixture at one full turn out. Started 1 kick & sat there at a perfect idle.
Went for a ride. Didn't feel right. Stopped & came out a 1/2 turn on the mixture. Felt happier. Ran well around town under all RPMs AND out on the road at 50 in 4th & 60 in 5th. It's running really, really well again & going between buildings is eargasmic.
Came home & the idle drops to dead low in less than 1/2 the time than before PLUS the engine now reacts to the mixture screw way better than it did before. I came out almost another 1/2 turn & the idle increased. I dropped it again with the idle speed screw & left it 'til tomorrow. I think I just need to concentrate tomorrow on finding that perfect mixture screw position & I will be home free.
If not I can throw another shim in in 10 minutes & see what that does.
Thanks guys. I've really enjoyed the process of learning this Mikuni (& the whole bike) which I've been doing since December 2010 when I bought this never-sold, not running, dry as a bone, no electrics, all bulbs blown, orphan '08 Classic. I knew nothing from nothing about this bike. And I couldn't have done it without Pete Snidal & whining to all you guys ad nauseum.
PS: I have no problem leaving that damn collar on the needle alone & using shims. I think there are 3 in there now. If I move (or remove) the collar now, I'm back to square one in finding my correct needle height using the grooves again, and shims. (For those reading this who don't know - this hard plastic collar on the needle of the BS-29 covers the 2 lower height grooves on mine. As I have freed up my intake & exhaust I've raised the needle progressively using .002" shims under the plastic collar. My needle is 3 shims (at least) higher now than it would be with an e-clip in the bottom groove). This carb was created to give an engine just barely enough fuel to run on, hence AVL Lean Burn.
Those carbs (BSs) were on bikes (Soozookies for one) & other small tools back in the '80s. Whose idea was that solid collar on the needle? Was it a Federal emissions thing? It must have been because the mixture screws were also plugged or capped in those days.