Author Topic: What's this for?  (Read 646 times)

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Offline SurfinBird

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What's this for?
« on: July 11, 2011, 07:48:33 AM »
'78 CB750F

Been having fuel starvation issues so I pulled the carbs for a really good cleaning. While I was doing that I noticed something. There is a nipple next to the fuel intake linking the carbs with small fuel tubing, I have no idea what it's for (breather?). I didn't really think about it until I noticed that the tube going from the #3 to the #4 wasn't connected, I got a replacement #4 from here and didn't notice the nipple on the #4 isn't there and the line isn't connected to it. Take a look at the shots. It's a little hard to see because of the shadow, but the tube isn't connected to #4 at all with about a 1/4" gap. there is a hole where the nipple was supposed to be.

Shot 1- fuel intake and mystery line
Shot 2- Normal connection carbs 1-2/2-3
Shot 3- connection in question, no connection from 3 to 4

-What is the line for and does it add to my fuel starvation issue?

By the way, the carbs were pretty clean. What would slow fuel delivery from the tank to the carb? New petcock, removed the inline filter, re-cleaning the carbs now.

Offline Johnie

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Re: What's this for?
« Reply #1 on: July 11, 2011, 08:25:50 AM »
Pics 2 and 3 are showing vents. They are between carbs 1&2 and also 3&4. You are correct the nipple is missing and is probably stuck in the vent line that was removed when you disassembled them. Find that nipple and push it back in as you do need those connected. Is there a chance you did not get the carbs back in the correct order on the rack? I am thinking that nipple in the first pic is maybe the one that is missing in the last pic?
« Last Edit: July 11, 2011, 08:30:38 AM by Johnie »
1970 CB750K0 - Candy Ruby Red
1973 CB750K3 - Candy Bacchus Olive or Sunflake Orange
1970 Chevy Chevelle SS396 - Cortez Silver
1976 GL1000 Sulphur Yellow

Oshkosh, WI  USA

Offline SurfinBird

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Re: What's this for?
« Reply #2 on: July 11, 2011, 08:59:10 AM »
The first shot is a top shot of where the fuel line goes into the carb and I guess the vent, when I bough the bike it had a thin hose leading to nothing (both on #2). I got a #4 carb from another member (my original had a stuck idle screw that was thrashed in the body) and didn't notice the vent nipple was missing. What issues would not having all 4 carb vents connected present?

Offline SurfinBird

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Re: What's this for?
« Reply #3 on: July 11, 2011, 10:46:49 AM »
After some research, the lines i'm questioning are the vent tube. Now, how does it affect the carbs if they aren't all connected and the vent line is not closed?