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Can you tell where the other end is attached to as that would be a big help.  With the bike running, do you have vacuum on the line or pressure? It is possible it goes to #2 carb vacuum port and then up to the pressure sensor for the ignition system. There might be another hose hanging down that this one connects to which would explain the tube it is connected to presently.

If you dont have a service manual for the VR MK2, here is a link to it and that be of some help to you.  https://www.venturerider.org/manuals/1986-1993 Yamaha Venture Service Manual.pdf

Let us know if you have more question or what you find out please.

Rick F.

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I agree it looks like the vacuum hose which goes to the vacuum port on cylinder #1. which is the second cylinder back on the left side of the bike. There should be a second short hose going from the fitting in the hose in the picture to the tube on the carb. If you look at carbs 2,3 & 4 you will find the same tubes  on those carbs have a black rubber cap on them which is not used on  cylinder #1 because the hose goes there instead.  Often times you will see this hose connected to cyl #2 which is the forward cylinder on the left side because some mistakenly think the front cyl is #1 . But to be honest I can,t say that whether it is attached to #1 or #2 that it made any real difference in the running of the bike.

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I got a chance to look this evening and I couldn't see any obvious hose or missing connection. I can't really see all the carbs.  Do I need to take off some more parts to get a good look?  I have attached some more pictures. The hose is running from the back of the bike. 

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@vulcanb822Now that I can see it is on the right side of the bike running along the frame you can disregard my previous post since I assumed the initial picture was of the left side.

It is not the coolant overflow drain line as that is the clear tube in the picture. That black hose most likely connects to the bottom of the rubber boot around your fuel tank filler neck. Its a drain tube in case you overflow the neck while refueling. You will find the nipple for it at the bottom left front corner of that boot.

Edited by saddlebum
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Glad you found the home of the cable. Now your question about backfiring is most likely caused by a bad air cutoff valve in one or more of the carburetors.  They might have a hole or tear in the rubber diaphragm that is letting air in.  These are available separately from different sources but it might be time to check all the carbs for these valves and also for tears or hole in the carb slider diaphragms. This are behind the large covers that you see facing the outside of the carb array with the 4 retainer screws. Check some of the forum post on these should help you understand them.

Good Luck..

Rick F.

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