does a carb breath in or out or both?
 

i was thinking or routing all the carb and fuel pump breather hoses (bar the drain and overflow) upwards into the airbox on my 1vj tenere. will the negative pressure in the 'box affect the carbs at all? has anyone done this?
cheers.

I would NOT do that. You need atmospheric pressure in the float bowl and elsewhere to work properly. If the air box was OK, Yamaha would have done that, especially on an off road bike....

After having my bike dyno'd, the hoses used for equalizing the pressure in the bowl were not replaced by the shop, are these hoses necessary? Without these hoses will dirt and dust gain easier access to the interior of the carb? Mike

Those hoses are air vents and could suck in a little. I always run mine. You can use clear hose available at hardware stores, very cheap.

In general I'd agree with that but there are always oddball exceptions. I'm running a CCM600 single with a DellOrto carb and if the breathers are anywhere but in the airbox the engine misfires briefly in conditions where you're hit with a wall of air - like overtaking a truck at speed for example and you go through the bow wave. A misfire at that point, when you're level with the cab, doesn't make for a relaxing ride :thumbdown:

I'm sure that Mikunis etc are not that sensitive (or none of the ones I have on other bikes are anyway) but the breathers do actually do something even if on "properly" designed carbs you're unaware of it.

I've always assumed that they deal mainly with any overflow from the float bowl, taking the volatile fuel away from the hot engine and down to the road level - I guess I came to this assumption via the number of times suchlike happened with my TTR600 carburettor. doh

looks like im gonna be getting/ making some kind of filter for the breathers then. i also got a 1 way valve for the overflow. the bike sucks in water in deep puddles and in dry conditions a bit of dust finds itself into the carb through the breathers....