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I have a 1995 Ducati Monster M600. Recently I noticed an engine vibration and whilst trying to figure it out I noticed that the horizontal cylinder exhaust is hot (hot enough to burn leather gloves) whilst the vertical cylinder is warm to touch.

My thinking is that the vibration is caused by the cold cylinder not working as hard as the hot one.

Checks so far:

  1. Fuel in oil - no smell of fuel in oil
  2. Unspent fuel in exhaust - no smell of fuel in exhaust
  3. Vacuum at Venturi in carbs is low on vertical cylinder on idle - under full throttle vacuum is good
  4. Theres no popping/banging on closing the throttle - i.e. no fuel getting into the exhaust
  5. Did the timing belts just over 1000 miles ago
  6. No issues starting the bike - bike fires every time within a second of pressing the starter button.
  7. Pull HT Lead on hot engine from cold cylinder whilst running to see if the vibration changes - pull from vertical cylinder leaves engine running, pull from horizontal stops engine
  8. Pull HT Lead on cold engine from cold cylinder whilst running to see if the vibration changes - pull from vertical cylinder leaves engine running - drop in 300rpm, pull from horizontal leaves engine running - drop in 300rpm
  9. swap ignition control units - engine still runs as normal - HT Lead pull results in the same engine stop on horizontal pull and engine run on vertical pull.

Checks to try

  1. Compression Check on cylinders
  2. Carb balance & synch
  3. check spark plug condition
  4. Check timing on cold cylinder

History I had a small fuel leak which caused the bike to run lean for a while but since that was fixed it had been fine. The fuel leak was at the tank feed to the fuel filter causing air to get into the fuel line.

Initially I thought it was a bad battery so I had changed that to a new OEM 12v lead acid battery.

I've also recently changed the front and rear sprockets from 15:41 to 15:43 which has probably made the issue more noticeable as the revs are slightly higher at any given speed.

Am I missing anything else?

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2 Answers 2

Sounds like you are not burning your mixture in the vertical cylinder, and the warmth is transfer from the horizontal cylinder. The vibration is usually can be caused by said dead cylinder, and the difference in force in the strokes creates an off balance in your crankshaft. This happens in motor vehicles as well, and its normally caused by a lack of combustion. Is the cylinder getting fuel? Maybe that's why you don't smell it, and explains the lack of combustion. Your checks back up the theory, since the bike dies when the horizontal cylinder is taken away. I recommend investigating the parts that cause the combustion (plug, fuel, or compression). Once the guilty party is identified, it should resolve all your issues.

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Yeah - new jets and needles are ordered - on choke it burns fine (as can be seen by pulling the ignition lead from the horizontal cyl and the bike continuing to idle ok) on open throttle it runs again on the cylinder...its just idle thats not right –  Mauro Aug 5 '11 at 4:43
up vote 1 down vote accepted

Found the culprit the jets were fine, however the float bowl was full of residue and water, as well as the jet carrier bolt being snapped in half so the jets were moving along to where they were not able to fuel the cylinder. After a full strip down, rebuild and calibration its now firing on both cylinders correctly.

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