fosdyke Posted July 15, 2007 Share Posted July 15, 2007 Hi Hope someone can help me with some ideas. I have a 1989 YB100 purchased from ebay and lovingly restored over the last 2 years including new bearings oil seals etc. It has been running reasonably well until about a week ago, when it started 'breaking' spark plugs - a new plug would run for only a few miles and die - ie weak or now spark. The colour of the plug was dark grey/black but not oily suggesting a rich mixture. I adjusted the carb and oil pump to try and acheive a leaner mixture - but no success, and today on a ride out it went through 3 plugs and finally died completely and had to be trailered home! An initial strip down indicated damage to the piston by a plastic substance which could only be the induction disc valve. Sighting through the induction port seems to comfirm this - so I have a job to replace this as well as the piston, with possibly a rebore as well! There may be another cause of the disc valve damage which I may find on further dismantling, but has anyone heard of this happening before - and was the 'plug destruction' a symptom of the impending failure? I am interested in any thoughts on this and how to improve the mixture settings on this bike for th future. Thanks Geoff Link to comment Share on other sites More sharing options...
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