i would say it is a bit low on compression,once it has been started does it usually run ok until its been left overnight ?does it have a manual or auto choke as this model was fitter with both depending on the year,i think the older ones were all manual choke but later ones are auto choke.Also one other problem these suffer from is the head gasket leaking on them .The head gasket on these are made of rubber and they not only keep the pressure in the combustion chamber but it runs around the water jacket and the studs in the barrel and head to stop coolant straying,if it gets on the spark plug it will foul the plug and stop it starting.so if you take the plug out can you have a look to see if it is wet at all?if it is then i would put a new head gasket on it in fact i would do it anyway on one of these , they are not dear but whatever you do make sure yoiu buy a genuine gasket only from yamaha all pattern ones seems to turn to bubble gum after a weeek or two.let me know how it goes.cheers adam.
adam bike doctor(of milton keynes motorcycle centre)
January 2011
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