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Discussion Starter #1
Alright, well my 2003 999 has developed a stumble while I was away from it for the past few months. It was started and run at least once a month by my brother while I was gone. Anyway here are the symptoms-

The stumble occurs when I am riding and try to pull in 6th or any gear that is fairly high from say 25mph or so in the 2500-4000 rpm range. It doesn't want to die, but the engine feels like one of the cylinders quits and then starts again. This mis/stumble never happens at idle when I rev it, just when the engine is under load. Any idea guys? The bike has almost 12,000 miles on it, just changed the fuel filter, and will adjust the valves, change belts, spark plugs, and sync the throttle bodies. I might put some fuel injector cleaner in the tank next fill up too, is there any simple way to clean the injectors while they are off the bike? As in what solution to use for soaking? Oh, the engine is stock, except that it has a small breather instead of the factory oil breather box. Yes, I plugged the airbox holes.
 

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your in 6th gear at 25mph and it ''stumbles''.i'd downshift bout 4 or 5 times and try it then.fwiw the coils have been known to have issues.(and part # has been upgraded)
 

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At 25 mph I'm still in first. I'm not in sixth unless I'm running 80 for a long time on the expressway. Normal riding has the first four gears used, but that's about it. The bike wants to rev above 4k and seems happiest there.
 

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If its intermittent, meaning it really shows up at one spot in the RPM range, it could be a lot of things. My reading your original message, sounds like you have NOT done the valve check and belt's yet. If you haven't done that, I'd go ahead and do that because the problem your describing could very easily be valve mis-adjustment.

After you've done that, the next thing would be to check the coils. Per a previous message above, Ducati did replace those and you do have the oldest generation.

Otherwise, there isn't much else that can go wrong... You could be loosing voltage at higher RPM because the regulator could be toast? I mean the list of "maybe" is very high on this one. Thats why for the diagnostic procedure, its wise to take out as many variables as possible.



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while I was away from it for the past few months. It was started and .
how many months? if it's been 6 or more and you didn't add fuel stabilizer, your fuel may be the culprit here. Gasoline breaks down.

Flush the system and start with new gas first.

BTW, 6th gear at 25mph. Really?!!!
 

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Discussion Starter #7
The bike has had fresh gas put in it every month. The stumble does not happen at high rpms, just in that range. 25mph in 6th, may be lugging it, but the motor should still not stumble and feel like it's transforming into a dualsport single. But there are a lot of variables and I'll see what happens after the valves and belts are done. I'm just concerned about a random problem like this developing. Maybe its just some water condensation in the front coil. Guess we'll see.
 

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Dude! Why would you do 6th at 25mph? I don't even go into 6th unless I am going above 85...or More!!! Sometime over 110mph.

Lugging? ya think!

Try staying in first at that speed and I'm sure your stumble problem will not be there.
 

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25 mph in 6th is only 900 rpm.

This is beyond lugging. This is below idle speed. It will feel dreadful. Period.

If the bike has good plugs, fresh gas and feels good at normal RPMs everything is fine.
 

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Really Robbie its not the bike. my bike doesnt even like going into 5th at 60 and I have a 14t front and a 42 rear sprocket combo. It had a 36 on it when i got the swingarm put on it and that really sucked. The only time you need 5th or 6th is at 65 or above. Your Busa might pull 6th gear at 25mph but the Duc wont.
 

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Granted, mine is an "s" model with hotter cams but it runs like crap below 4K RPM. I did, however, have a stumbling problem between 4-5K RPM that ended up being my throttle bodies out of sync. My mechanic (Scott at Motoservizio) said that it's quite common for the 999's to have out-of-sync throttle bodies by the 6K mile service.
 
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