650ed wrote: Here's a picture of where the two vent tubes terminate on my KZ650-C1. Their ends terminate in the air filter opening. Ed
I've never seen a factory bike with vent tubes going into the intake mouth. That puts the vent tubes under changing pressures. I've always seen the factory tubes just open ended just after that plastic holder (baffle plate) for the tubes. Near the mouth of the intake or closer to the battery, but never inside of the intake.
Looking at the factory manual for the 77 Kz650, page 41 shows the vent tubes going past the air intake and to the battery box area. Page 42 says "Route the carburetor vent tubes (2) to the battery housing sides between the air cleaner housing and the baffle plate"... not exactly clear on what they mean, but it seems the hoses are meant to go to the battery box area.
When I was doing jetting tests, and was doing a fringe test on the lean side, just moving the vent tube out into rushing air was enough vacuum to cause a hesitation. I would think a similar issue would happen with having the tube in the mouth of the intake. Under normal jetting it might not hesitate, but will be slightly leaner than designed. More importantly, the amount of pressure will change with throttle. This will alter the bowl pressure with throttle. That introduces another variable that did not exist before. If the factory had intended for the bowls to be vented to intake mouth pressure, I think they would have created a hookup port on the filter holder of some sort.
I just try to route them into an area that will have still air, but not in a sealed off area. Near the battery box or up under the tank is usually good.