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Discussion Starter #1
Hello everyone, I've been around for some time, but this is my first post here.

I'm helping out a friend of mine. He's just bought a M600 2001 or 2002 (last year of carburettors before ie). 6.500 miles. Free flowing, noisy exhaust and (probably) rejetted.

It has had some carb-problems. First we thought it might just be the cold, but it kept stalling, so he took it to a dealer. They cleaned the carbs, said they were dirty. It now runs a lot better.

But I can't adjust idle.

When adjusting idle screw to 1500 rpm (it won't go any lower) and revving the engine to 5000, it first drops to 2500-3000 and 10 seconds later drops reluctantly to 1500.

If the idle screw is a mere 1/4 turn higher, the idle leaps to 3000 and more.

When fiddling the balance screw one turn to either side, the idle gets faster. Is it normal?

When administering sudden choke/fast idle, rpm will drop radically, sometimes the engine stalls.

So I figured this might be the setup:
The carbs are mixed too rich. The idle screw is far under normal setting. However there is _a lot_ of fuel, this makes the engine idle, and any extra air will make the engine rev up, because of the extra air, and a better mixture.

So I'm going to attend the mixture screws, then syncronize the carbs.

But I also figure that the rich condition might come from oval needle jets.

Am I right here? Any ideas? What should I check?

I would really like to know stock settings and jets, and what to look for to identify what kind of rejetting was made (I'm probably going to pull the carbs to check for oval needle jet).

Sorry for the rambling...

5 Posts
definately sounds like a jetting problem. I would re-jet to stock (sorry I don't have the sizes for that) and go from there. Also I would check to see how good of a job they did cleaning the carbs. just my .02

3,931 Posts
There are two things that I know of that will make it idle fast for a while, then drop down. One is some sort of air leak between the carburetors and the engine. The other is when the carburetors are out of sync. I had that problem on my ST2 (with fuel injection) before I took it in for a service. Synchronizing the throttle bodies totally fixed that problem.

At idle, the needle jet should have no effect on how the bike runs, so you can rule that out.

Premium Member
115 Posts
The stock setup is :
Main jets :132.5
Pilot jet :40
Needle position #3
Mixture screws : 2,5 turns out from fully seated (you can go with 3 turns for better starting when cold)

If you have an idle problem the only thing that can affect that is the mixture screws .Synch the carbs anyway .You can find good advice to www.ducatisuite.com
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