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Discussion Starter #1
I'm working on fixing a leaky vertical cylinder, and in order to access that cylinder I've had to remove the airbox and carburetor on my 2001 Ducati M600. I have the carb sitting on my desk now, and I'm wondering what all I should do while I have it out like this? I opened the bowls and checked the 3 jets in each bowl and they appear to be clean. I don't see brown tarnish inside of the bowls. There is a small bit of white powdery stuff but not much. The diaphragms seem soft and malleable.

Is it worth doing anything else? Should I spray carb cleaner into where the jets go? Should I disassemble it and put it into an ultrasonic cleaner (I have access to some at work)? From the outside it looks clean, but I know for a fact that it has been at least 3 years since the carbs were last cleaned, then it sat for a while. However, I put 6k miles on it over the course of a few months, so I'm thinking that just riding it a lot may have been enough to clean it out?

Any general tips would be greatly appreciated. I'm also not against ordering some new o-rings and/or jets if that could somehow help.
 

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As long as it’s already off, the minimum I would do is spray all the passages and the venturis with carb cleaner. Screw your idle mixture screws in until they lightly seat, counting how many turns so you can duplicate the adjustment Then take them out and spray cleaner in the hole. Make sure you have a good spray coming out both in the float bowl and out of a tiny orifice in the carb throat. A sewing needle can be used to unclog that orifice. New o- rings for the mixture screws wouldn’t hurt. Wear safety glasses, it can splatter. Replace the o-ring under the diaphragm cover and be careful that the diaphragm stays in its groove as you put the cover back on to avoid ruining it, they’re $80 each.
Personally, I would rebuild the carbs completely, but if you aren’t comfortable I wouldn’t try it. If you do, Factory Pro is the tuning kit I’d recommend, with titanium needles and nickel plated emulsion tubes that wear much better than stock and get rid of the rough running some people experience in the 3000 rpm range. You will also need rebuild kits because there aren’t any gaskets in the Factory Pro kit, it’s a tuning kit with jets, etc. if you pull anything on the carbs apart I would recommend replacement gaskets and o-rings to avoid leaks. I don’t like doing it twice. If you go this far you’ll want to adjust the floats. There are YouTube vids for this stuff. Take pics as you go to help with reassembly . I use an iPad , bigger screen. Good Luck.
 

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Discussion Starter #3 (Edited)
I see that there are three jets. A, "main jet", a "Starter Jet" and an "Idling Jet".

How does the carburetor "select" which jet it will use? It seems like the jet with the largest "bore" would always dominate the two smaller ones, sort of like a small resistor in parallel with two large resistors?
 

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The starter jet is selected by the choke lever, to “add” some extra fuel for start up. The pilot jet gets fuel siphoned through to an orifice in the bottom of the venturi. It’s very tiny so a small vacuum like at idle or small throttle opening will start pulling fuel through it . When the throttle is opened further, the needle starts to rise allowing vacuum to pull fuel through the main jet, increasing in volume as the needle lifts and exposes it.
Think of it like trying to suck liquid through a cocktail straw. Very little effort required. But that same amount of effort will not pull liquid through a garden hose, you’d have to suck much harder, like the engine does as you open the throttle. Remember your engine is really a big air pump. The throttle controls how much air flows through it. They do overlap, that’s why there is a needle that is attached to the slide that unplugs the main jet progressively as you raise the slide with the throttle, allowing more flow. Simple, huh ?
 

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Discussion Starter #6
The starter jet is selected by the choke lever, to “add” some extra fuel for start up. The pilot jet gets fuel siphoned through to an orifice in the bottom of the venturi. It’s very tiny so a small vacuum like at idle or small throttle opening will start pulling fuel through it . When the throttle is opened further, the needle starts to rise allowing vacuum to pull fuel through the main jet, increasing in volume as the needle lifts and exposes it.
Think of it like trying to suck liquid through a cocktail straw. Very little effort required. But that same amount of effort will not pull liquid through a garden hose, you’d have to suck much harder, like the engine does as you open the throttle. Remember your engine is really a big air pump. The throttle controls how much air flows through it. They do overlap, that’s why there is a needle that is attached to the slide that unplugs the main jet progressively as you raise the slide with the throttle, allowing more flow. Simple, huh ?
Great explanation thank you. I've come up with some new questions though about where the fuel comes from before hand... if you don't mind tackling another one.

Is it correct that the fuel goes from the fuel tank, through the fuel filter, through the petcock, through the fuel pump, to the carbs (via the tube labeled 13), where it flows into the bowls via the float valve mechanism?

If so, what is line 7, which goes from the petcock directly to the carburetor? It is labeled "Fuel Chock / Inlet duct pipe" in the parts manual.

Picture here:

https://i.imgur.com/j6uIiuz.png
 

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Stump the old guy ? Actually, I’m not sure , though I’ll hazard a guess . I’ve never had a carby Monster, I have a carby SS. I think your bike has a vacuum fuel pump rather than the electric pump on the SS. I think that is the vacuum line to operate the pump. Make sure it doesn’t kink or leak because that would reduce flow and could cause a lean mixture.
 
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