youre half right , The carb mixes the air and fuel before it enters the engine, what rought surfaces do is help break surface tension on the droplets of fuel and allows it to atomise more readily.

You don't have to worry about it-normal engine is designed the way that if you pull cranck forward to front bearing it still will have clearance on the main bearing to avoid binding
See attached pic- I tryed to make it visible with 2 arrows pointing on front bearing with no clearance and main bearing with clearance. This is way how all engines designed (unless.....)
BTW this pic is fragment from real nitro engine design work. :nod: :nod: :D

Thanks Edward, you are the man. I understand completely
Nick Marson

anyone tried to sharpen the LSN? or even also the HSN?

Yes you can change the tunability of the needle by changing its shape . Tapering the LSN is common ..

oic, coz only recently some1 told me about it. but how can we sharpen it evenly?? do u use sandpaper or grinding stones?? to wat extend do we need to sharpen it to?

Ideally you would hold it to the side of a medium smooth grinding wheel and turn it evenly resting on an edge. Or with a dremmell you can use a pink stone flat turner, mount it and turn it onto the stone. As long as its even and smooth . You can finish it with some 800 wet and dry . Just bring the last 2 to 3 mm to a point then you can round the very end slightly.

is there any bad with this sharpening, like higher temp?

No, just a different tuning feel, and maybe a slighly more linear trasition from idle to mid range ..