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On the stock Mikuni carbs on my 900ss on the horizontal carb on the right side of the bike there is an uncapped brass elbow on the side of the carb. What is this? Also the fuel return hose coming from under the tank is wire tied to the frame but not connected to anything. Is that correct?
 

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Trying to visualise what the brass elbow could be - possibly an overflow?

You should have three pipe connections under your tank:



(not a great photo...:D)

The lefthand one is your feedpipe & should have a petcock on it, the pipe from this will go down by your vertical pot where it will join a Y-shaped connector, one tube from this will join your carbs, the other will go back up to your tank and fit on the middle "backflow" connector, returning all the excess fuel being pumped down from the tank.

The third right-hand connector is your overflow from your filler cap bowl, should be a smaller dia. tube running down the side of your engine to the floor?

Hope this helps? :)
 

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I don't recall the brass piece on the carburetor as I swapped mine out for FCR carbs a couple years ago at this point. But the connections on the tank should as follows...The feed and return lines connect together at a plastic 'Y' fitting about midway between the tank and carburetor inlet fitting. It may seem an odd looking arrangement until you realize that stuck into the hose on the return side is a small brass piece that reduces the effective diameter of the hose from 7mm to 4mm, creating a pressure differential, and so crudely setting the pressure of the fuel that travels down the third leg of the Y fitting to the carburetor inlet. On my bike this small brass fitting was pushed in the hose on the return side next to the Y fitting.

It already sounds like someone has botched up your bike's fuel system. Does it still have an electric fuel pump? The only way you wouldn't need the return line is if you discarded the electric fuel pump, but then you wouldn't be able to use the tank's full capacity.
 

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evap (?)

on the hor carb of my 96ss/cr, there is a brass-colored elbow pointing down, connected to a rubber hose. this hose has an in-line backflow valve, and is connected to a black triangular-shaped box on the bike's left side.

there is an identical line coming down from the vert carb also going to the box. from the box is a smaller line going back up somewhere between the carbs.

part of the evac system i think, but not shown in my manual. looks like someone cleaned up the "extra" stuff on your bike. was going to do the same on mine but was worried that there might be small vacuum at that elbow, drawing in dust/what-not to the carbs. or maybe there's pressure instead of vacuum? no idea.
 

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On the stock Mikuni carbs on my 900ss on the horizontal carb on the right side of the bike there is an uncapped brass elbow on the side of the carb. What is this? Also the fuel return hose coming from under the tank is wire tied to the frame but not connected to anything. Is that correct?
Those two brass elbows are actually carb vent ports, meaning they can't be capped. Stock settings have a black hose (with a spring around it to keep it from kinking) coming from those elbows into those little black triangle boxes on the left side of the frame as standswithabeer said. These hoses need to be vented into STILL AIR, that's why they go into those boxes. If the hoses are just left hanging, (or there's no hoses on the elbows at all), the resulting opening may be in the airflow of the moving bike, thus creating a vacuum at the ports. Of course, this effect may be different on full and half fairing bikes.

Sounds like someone just pulled those hoses off in an attempt to clean up the bike. If it's running well, might as well take off the black triangle boxes too and clean up the frame. Hope that helps!
 

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Discussion Starter #6
Thanks for the info. Punch455 has it right about the elbows on the carbs. I found an exploded diagram of the Mikuni which shows the missing hoses with springs though I haven't replaced them as of yet. I also added the y connector in the tank lines.
I should have put more info in my original post. I bought the bike which is a one owner trade from a BMW dealer. It has 5400 miles on it. Mods on it at purchase are Micron exhaust, open airbox with K&N, and Stage one jetting. The carbs had been rebuilt once in 2005. The bike has a high rpm (over 6000) sputtering and backfiring problem. I replaced the in-tank fuel filter, plugs, wires and coils. I then took it to a Ducati dealer who cleaned the carbs, replaced some gaskets and adjusted them but the problem still remains. These are the issues which had me looking at the carbs ansd hoses mentioned in my original post. I'm just trying to get it to run cleanly throughout the rev range.
 

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I'm in darn near the same situation as you are. I just bought mine as a two owner trade-in, low miles and has the same problem, breaking up at higher RPMs. Though, I can't confirm the jetting until I go through the carbs.
 

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on the hor carb of my 96ss/cr, there is a brass-colored elbow pointing down, connected to a rubber hose. this hose has an in-line backflow valve, and is connected to a black triangular-shaped box on the bike's left side.
Those 'backflow valves are actually filter, fairly course ones, but filters all the same. Try giving them a clean.
 

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The bike has a high rpm (over 6000) sputtering and backfiring problem. I replaced the in-tank fuel filter, plugs, wires and coils. I then took it to a Ducati dealer who cleaned the carbs, replaced some gaskets and adjusted them but the problem still remains. These are the issues which had me looking at the carbs ansd hoses mentioned in my original post. I'm just trying to get it to run cleanly throughout the rev range.
Hey I just noticed you're in Orland Park. I'm on the North side of the city. In the ducati world, we're practically neighbors.

As far as the sputter at high rpm, does it happen at certain throttle inputs? Like WOT, 1/2, or 1/4 throttle turn? You can narrow down jetting problems that way. If it happens at all throttle inputs, then it's likely a fuel supply or ignition problem.
 

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This is a link to the workshop manual which has a huge section (Section O) on Mikunis, set up etc.

Page A8 shows the arrangement of the fuel system at the tank.

The file will not be there after 30th June 2012 as Apple are moving to iCloud.

It is multi language which is why the file is 188MB

Download speed will be relatively slow.

Clicking the link below will start the download.

Richard

https://files.me.com/yellowducati/c6t4cm
 

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Those little filter screens are not adequate. Those hoses need either a better filter or maybe route them to your filter box, if you have one. Mine sucked in a lot of dirt in just a few miles.
 

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Discussion Starter #13
The poor running seems mostly related to rpm rather than throttle opening although the more gas you give it the worse it seems to gets. I've got it at a local (South Suburban) shop that have worked on my bikes before so I should know in a couple of days whats up.
 
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