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...
pfcdaz Posted July 16, 2007 Share Posted July 16, 2007 can't help you with that i'm afraid although i will certainly bear it in mind if a similar thing starts to happen to mine. i am restoring a YB100 myself and if you have read any of my other posts you will see i am having a complete nightmare trying to get the forks in working order. when you did yours did you have to replace the fork seals? and if so, how in gods name did you get them back together again, as far as i can see you have to compress the fork to get the top bush in far enough to tap the oil seal down, but that means i can't get a bit of tube over the stanchion to tap it in with. any tips? Link to comment Share on other sites More sharing options...
fosdyke Posted July 17, 2007 Author Share Posted July 17, 2007 can't help you with that i'm afraid although i will certainly bear it in mind if a similar thing starts to happen to mine. i am restoring a YB100 myself and if you have read any of my other posts you will see i am having a complete nightmare trying to get the forks in working order. when you did yours did you have to replace the fork seals? and if so, how in gods name did you get them back together again, as far as i can see you have to compress the fork to get the top bush in far enough to tap the oil seal down, but that means i can't get a bit of tube over the stanchion to tap it in with. any tips? Hmmmm I was lucky my forks were ok - so beyond checking the seals I didn't dismantle any further, but I will consult the learned manuel to see if it has any tips. And as a postscript to my original post - having completely dismantled the engine I have found that it was big end failure that trashed the induction disc - and one half of the crankcase.........so I am busy sourcing a replacement engine...booo hooo. Still on the bright side I have more than doubled my array of spare parts!!!!! Link to comment Share on other sites More sharing options...
pfcdaz Posted July 17, 2007 Share Posted July 17, 2007 Hmmmm I was lucky my forks were ok - so beyond checking the seals I didn't dismantle any further, but I will consult the learned manuel to see if it has any tips. And as a postscript to my original post - having completely dismantled the engine I have found that it was big end failure that trashed the induction disc - and one half of the crankcase.........so I am busy sourcing a replacement engine...booo hooo. Still on the bright side I have more than doubled my array of spare parts!!!!! try MSR motorcycles in scarborough, (on the net) he had a complete yb100 for breaking, thats where i got my new forks from. not sure if the engine is decent or still available, but worth a try.... i have the manual but it makes out that all you do is tap the fork seals in, which deosn't seem possible when it is in front of you witthout about 4 pairs of hands Link to comment Share on other sites More sharing options...
fosdyke Posted July 19, 2007 Author Share Posted July 19, 2007 Thanks for the tip..........yes MSR did have one, and hopefully it will be delivered before the weekend, so if the engine is good it could be back on the road for the weekend! I did do the fork seals on an old RS100, similar to the YB, I seem to recall fitting them back in the bike first, but maybe my memory is fading....you could try that or putting them in a vice to free-up one pair of hands!!! Link to comment Share on other sites More sharing options...
danidge Posted August 6, 2007 Share Posted August 6, 2007 thats what my tzr kept doing before it completely stopped! it done like 30 miles to a plug im not having much luck with this bike. Link to comment Share on other sites More sharing options...
fosdyke Posted August 7, 2007 Author Share Posted August 7, 2007 New engine fitted and bike back on the road within a week - much to the 'other half's' delight! Danidge - check out my replies in the workshop forum! - BTW is your bike making any 'unusual' noises - loud rumbles that could indicate major mechanical wear? Link to comment Share on other sites More sharing options...
deenjay Posted August 7, 2007 Share Posted August 7, 2007 New engine fitted and bike back on the road within a week - much to the 'other half's' delight! Danidge - check out my replies in the workshop forum! - BTW is your bike making any 'unusual' noises - loud rumbles that could indicate major mechanical wear? the fs1e group use yb100 engines for their specials you will find all the help you need from them www.fs1e.co.uk Link to comment Share on other sites More sharing options...
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