Topic: Downdraft CV Carbs on a Ducati

[KB02]

Okay, so the problems that I have been having with my Ducati are still on my mind, and in essences, on my work bench.
Here's the basics: 2000 Ducati Monster 750. CV Carbs. The bike has been running richer and richer over the last couple of years to the point now that I am only getting about 1000-1500 miles out of a set of plugs before they get fouled out. I have been through the carbs and clean everything out and checked all passageways and everything. I could find nothing wrong. My theory now s that there is a vacuum leak somewhere in the tubing between the engine and carb bodies that's causing the rich condition (one that has gotten progressively worse), but then I found this:

In the jet tower assembly (pictured below) in the tunnel for the Main Air/Starter jet (Depending on where in the Haynes Manaul you read), there is a small brass plug/jet that sits under the jet. Normally, I would think that this brass plug keeps thing at a constant flow, BUT if this is to be a sealed area, there seems to be a leak around this brass plug/jet as I can see light from the other end around the side.

This is the Jet Tower as it sits on the carb with the flow pattern marked in red (The area the leak is coming from in blue):


This is a shot down into the tower. The top right hole is the one in question.


In this shot, the little hole in the middle (end of the blue line from the first picture) is where the light/leak is coming from.


Is this normal? Both carbs are the same. There is no way that I can see to get this little plug/jet out. My Haynes Manual is of no help what so ever. Anyone have any experience with these carbs?

[750essess]

At first I thought there should be a little ball bearing pressed in there to block it, but if you say they are both the same thats unlikely.

[KB02]

yeah, an there were now little ball bearings in the bowls either. I had thought about that.

[750essess]

found a diagram. Looks like that hole is supposed to be there

(Edit)it isnt displaying very well, l can email it to you if you want, let me know.

[KB02]

Sweet! Yes, if you could e-mail that to me that would be awesome.

I posted this message on a coupe of Ducati boards, too. On one of them I still have not gotten a response. The other was quite helpful. The guy who runs the board sells parts and accessories for Duc's, so part of his answer was a Factory Pro Jet kit that he offers for sale. It's $155, and looks good, and will probably be ordered later today. 

Thanks for the Diagram!

-Bob
KB02

[DME]

Is it running rich all the way through the rev range including full throttle?
Or is it just on low and mid rev range?

If it is on low and mid range, check your needles and emulsion tubes for wear.
The emulsion tube and needle on these CV carbs tend to wear as the throttle flutters up and down a bit creating a seesaw action.
This makes the needles grind away at the emulsion tubes, elongating the hole in the tube.
This in turn lets more fuel pass at low/mid revs/throttle opening where the fuel amount is controlled by the needle.
The problem will get progressively worse as the wear gets worse and worse, letting more and more fuel by.

At full throttle the amount of fuel is controlled by the main jet and the needle/emulsion tube-wear should not make a difference.

If the bike is stock jetted now and this description fits, replace your emulsion tubes and needles with stock parts before you buy a jet kit.

Cheers and good luck!

Dan

[KB02]

That's actually why I ordered this particular jet kit; it includes Titanium Emulsion tubes and Needles.

Somewhere along the line, late last summer, my Ducati being my daily rider and my Honda being my Daily tickerer switch roles.