OK... here it is:
I'm not sure I have enough knowlege to write about carbs. I wouldn't have posted the questions starting this thread if I knew much about them. Feel free to use what I write here to start a new thread. I have noticed a few interesting things with the BST. Since I do wheelies regularly, I noticed that sometimes the bike loses power when the front wheel is up. Wheelies are then impossible to control and instead of looking cool, it looks like I'm struggling to stay in charge...(and that's not good when you're riding on one wheel). When that happens, I know that it's time to look inside the carb. I hate taking the carb off the bike, even thoough it's quite easy and with a little practise doesn't take long at all, so I usually just unscrew the 2 screws on top of the carb to get to the vacuum cylinder and take it out with my fingers. That alone will in some miraculous way improve the performance of the bike (after you put everything back in the carb, of course). But since it's out, clean all the dirt that's in there. Usually there's enough to see it clearly. After that's all clean, put everything back together and go riding.
The bike will run smoother, in most cases it will eliminate some of the popping on decceleration and...
When there's dirt/dust in there, sometimes when riding at very low steady revs (e.g. in traffic in 2nd gear) I feel that the power delivery is not smooth and there are "fluctuations" in the way power is delivered. If I'm not moving the throttle at all, the revs should be steady and I shouldn't feel any roughness. Unfortunately that's also one of the hints that it might be time to take a look in there. I've had a 640 for 5 years and it does happen from time to time. Use whatever you want to clean the inside of the carb. Q-tips work fine.
I'd recommend cleaning tha area of the carb at every check up (5000km / arnd 3000miles).
Smooth power delivery of the BST helps in a sense with wheelies. It may be easier to do a wheelie having a pumper carb because of the better throttle response but after drilling the holes in the vacuum cylinder I can't complain. So if you have decent throttle response to start a wheelie, it's easier to continue it having smooth power delivery. If it's too snappy, it might be more difficult to control. On the other hand, everything is only a matter of time and practice. There are people who supposedly wheelie GoldWings !!!
Well, I guess I could start a wheelie thread with some advice for those who'd like to actually learn, not destroy their bikes and health... I've read the forum from time to time but can't be sure whether threads like this have appeared here (and how many of them) so I was going to be careful with what I post :)
If someone with as many posts as you meat popsicle thinks it'd be useful and fun, I'll get to it...
Back to the carb... the smoothness of power delivery of the TM40 I had on my bike was amazing. I have no idea if it was properly adjusted or not. I had no time to mess with it enough. I don't know if every TM40 delivers power the same way, but it seemed you couldn't rev it too low. Normally in 5th gear th lowest speed that the LC4 engine accepts if you want to accelerate is around 80kph. On TM40 I could get as low as 70kph and I didn't hear any strange noise or feel the usual vibrations when speeding up. I can't say the engine was super powerful down there. It was just.... different and kinda cool. Definitely much, much better than BST. I guess that if you consider that it also improves the performance a little and properly adjusted adds more snap, then it's definitely a nice thing to have and even nicer to use.
I imagine that throttle response doesn't change with a stiffer shock. The grip might change but only in the dirt or loose stuff. As you already know, I don't go offroading that much. I simply have no time. I even have another set of wheels all ready to go...
One more thing about the BST I just remembered... Imagine you're doing a stoppie with the BST. When the rearr wheel goes up, the engine stalls and there is a little puddle of gas under the bike. The hose that the gas spills through is the same one used to drain the carb - at the very bottom of it. I don't have this problem because Instead of letting it go straight down and through the zip-ty by the swingarm axle, I put it up and around the main gas line (the one from the tank to the carb) and then down where it normally goes (it's long enough to reach). There you go - no gas spills or engine stalling