Originally Posted by bmwktmbill
Beek and Timo,
You are both right.
About carbs and flow I really don't know.
Hey that rhymes.
I go back in time to the flow bench and Sonny Branch making Harley's go fast on the flat track.
Out of all that I got it that air is an invisible, compressible fluid.
So birds fly and so do airplanes and I always loved the look of a velocity stack.
Air flows like water. It's a fluid. Birds swim in the air.
Being a fly fisherman I spent many years of time watching water.
It flows and is predictable in my experience.
That said, we understand that KTM used a BST on the 640 travel bike because the Adventure was not designed as a racer. The BST is a carb that self adjusts to altitude changes and is a frugal user of fuel.
If I was running a FCR carb on a 640 Adventure I'd have to see the layout of the 660 racer's airfilter and airbox, I'd build that as best I could....
The factory always cheats.
They use a dyno.
As for dirt, no worries, chrome bore and chrome rings.
The foam filter in my experience doesn't pass dirt, it will plug eventually but it is easily cleaned with tank gas and oiled using a bread bag, engine oil and some EMT gloves.
So many words of wisdom here.........I forgot the name "Sonny Branch" and all the flow bench secrets that man revealed.
For me......my BST with only 3000km's on it works fantastic!........I'll use it until it gives me problems then I will install an FCR because I don't change altitude that much.
As for dirt........the foam air filter only gets more efficient
the dirtier it gets.........all you have to do is clean it to get more performance!
HP2 Sport, R1200S, R100S, KTM 640 Adventure, KTM 520 EXC/Motard, Yamaha RZ350, Hodaka 125 Wombat