Hanging rpms with terrible idles

[data10019]

been on the hunt for what i assume is a vaccum leak; rebuilt the carbs and still had the issue of the bike idles then you hear a very quick drop like its goinna die but super quick and keeps idling. THEN if i get random rpm spikes and some crazy rpm hanging which if i do a blip on the throttle clears it. I got this bike a year ago and it had the same issue and havnt had time to do much with it. Last time i worked on it the non stock air filters caught fire from all the back firing.

Now I have oem air filters and rebuilt carbs, I feel like the back fires went away but looking through the forums i realized theres a tube that goes from crank case to air filter h-box.......The previous owner didnt have an h-box as i ordered that and he has this tube that goes no where. Now I see that this is a fucking engine breather hose that should be routed into it.

I cant test this until tomorrow but this is my fucking issue right? Just have this hose pointing up not connected to anything at the moment, surely this will cause a vacuum leak?

 

[CaptChrome]

Just have this hose pointing up not connected to anything at the moment, surely this will cause a vacuum leak?

Probably not. The crankcase is usually under a bit of pressure from a small amount of blow-by past the rings and that hose goes to the intake of the carbs so that the crankcase gases don't escape to atmosphere. The area where vacuum leaks cause issues is from the carb butterfly shafts to the inlet to the head. So, you are looking for leaking shaft seals, cracked or non-sealing carb holders, leaks at the vacuum nipples on the carb holders and leaks from the gasket/seal between the carb holder and the head.

 

[toddh9]

Check your butterfly/carb synch adjustment. Make sure both the springs are there.
My ‘77 was behaving similarly because there was some grit under the synch adjustment screw.