Topic: carb vent hose routing question.

[lostmykeys]

 I have a 78 cb750 super sport with the stock carbs airbox and exaust.
 The crankcase breather is not hooked up intead there is a small filter from the cam cover.
 I know that the carb vent should just hang down with the rest of the hoses but the carb vent on my bike is routed to the L shapped fitting on top of the airbox were the hose from the crankcase breather should be.
 Would this cause my bike to run poorly?

[iron_worker]

I'm not an expert but yes I believe this could have an affect. Your air box could have a slight vacuum and thus you're drawing a vacuum on your carb bowls. I believe this would cause there to be a smaller pressure differential between the bowls and and venturi of the carb and thus drawing in less fuel (run leaner). 

Also, if one of your floats sticks you'll be drawing raw fuel up into the air box which seems like a pretty big no-no to me.

Someone else may chime in here but what I said makes sense to me ...  lol

IW

[mono]

there was just a big thread about the "what hoses go on the airbox and what they do" ... does anyone have the link for that?  i actually need to re-visit that thread myself, as i noticed last night during re-assembly that my airbox lacked the bottom hose that's supposed to have the squeeze-valve AND the rubber "adapter" for the hose to the crankcase breather was all broken up and totally useless.

Lostmykeys:   from what i understand, all of those connections are important and will affect performance since everything carb-related seems to hang in a delicate balance with each other.  i think IW is right about vaccuum issues too.

[lostmykeys]

 so should I just plug the L fitting on top of the airbox?

[nayto550]

so should I just plug the L fitting on top of the airbox?

If the crankcase breather has been rerouted to run to open air with a filter, yes, block the airbox fitting it was on originally.  The only thing that should be connected from the carbs to the airbox is the boots that attach the carb intake to the box.

[lostmykeys]

 Good thanks,Maybe this is what is causing the flat spot at 4000 rpm and I wont have to tear into the carbs again..see my other thread.