Topic: routing carb drain tubes to the airbox and Bernoulli's principle

[Holden]

According to the Honda parts fiche, the rubber drain tubes that attach to the nipples on the bottom of the carb float bowls on my CB750K4 should be routed to holes in the bottom of the airbox.  Could this have a negative effect on performance by partially defeating Bernoulli's principle in the carbs?  In other words, wouldn't the drain tubes transfer some of the vacuum of the airbox to the carbs and therefore lower the velocity of air passing through the carbs and therefore reduce the amount of air and fuel getting to the engine?

Could someone smarter than I explain the performance effect of routing these tubes to the airbox?  It seems like an idea designed to lower emissions (I didn't think there was a concern about motorcycle emissions in '74) by reducing the release of unburnt fuel.  I'm all for reducing pollution, but if the floats are correctly set than routing the tubes to the airbox seems unnecessary and could only be a performance detriment.

[Gordon]

You sure you're not looking at the two vent hoses that come off the metal tubes between the carbs?  The float bowl overflow lines should never be connected to the air box.  Their only purpose is to route fuel from overflowing carb bowls down to the ground and away from the engine. 

[Spanner 1]

Gordon +1.......... bowl drains are intended to be just that...routed down between the swingarm and frame in case of bowl overfill.

[Holden]

Thanks.  This is my mistake based on another hack job done by the previous owner (he ran the lines to the airbox, probably his way of addressing a float set too high) and  my resulting misinterpretation of the parts fiche.  I'll pull the lines out of the airbox.  I didn't think it made sense.