mixture

Hi Guys
A friend of mine has a lady Dax that seized when I removed the head and barrel it had seized the piston , What I found strange is the combustion chamber and spark plug had a coating of soot has anyone had this before and why does this happen

Pretty certain this is caused by unburnt fuel.
Could be due to many reasons, bad timing, weak spark, lack of air due to dirty filter or even the choke stuck open.

Hope that helps

If has been standing for a very long time it will seize just by standing, my st70 had not been turned over for well over 20years and was solid, a good squiz of thin oil down the plug hole up end the bike briefly to oil right round the bore, leave over night , 17mm socket on the crank nut and voila! compression was low until the rings freed up but with the heat from a few minutes running the compression was where it should be, If it has seized through a weak mixture the bore will have pick up marks on it probably, A partially blocked main jet can give rise to weak mixture but I would imagine the bike would not produce enough power to pull itself along!!
Of course it may have been run very low on oil, and being a roller bearing bottom end the piston would have seized before the big end gave out.................
.......... Mind you, nobody would run low on oil..... would they?