carb popping out of bowl vent? backfire maybe?

78 1000 motor with stock 77 carbs. Got it running the other day and I'm not sure I have the vent lines plumbed correctly. I have the three vents on the side of the carbs vented into tubes running down to the base of the bike. Anyways, I have a pop or backfire coming from the #3 carbs vent hose. Not regular but pretty constant. What should be checked? Also, I can't find a "soft bottom" on the pilot jet screws, they feel stiff and difficult to tell where theyre at before binding the little spring.

....with stock 77 carbs.... I have the three vents on the side of the carbs vented into tubes running down to the base of the bike.......

3 vents on stock carbs?

+1 Ed

IIRC the stock carbs have 2 bowl vents ON carbs #2 and #4 and may have an additional port that is a vacuum port intended to attach to the vacuum controlled petcock. Again IIRC on the vm26ss carbs - which is what I think were stock on the 78 1000s - the vacuum port is on carb #3. If you have the vacuum port open - not blocked or plugged - then you have a vacuum leak and need to resolve it.

Awesome, that should be an easy fix then. I assumed they all did the same thing, vent, since they looked the same. I never had the bike or motor in stock setup. Should the other two, 2 and 4, be linked with a tube or vented to atmosphere?

The vents should be open to the atmosphere, as they allow air in and out of the bowls. As fuel level lowers in the bowls air must replace it, likewise as fuel raises in the bowls air must be removed.