my yamaha xs 650B is misfiring on the left cylinder when under load, i have replaced the coil, points look ok and the valve clearance is correct have read that if the cam chain has stretched it can cause these symptoms. can this be adjusted ? any help greatly apprieciated

keymatic, January 2012

i junked the points ignition on mine for electronic boyer-bransden-no more misfiring, did you fit new condensors if not, swap leads over and see if R/H side misfires, when's the last time the points were changed? sounds like a weak points spring-causing bounce leading to misfire at high revs, may as well fit new spark plugs too, try Champion N3 mine loves 'em!

Pitkin, January 2012

will check the jets and see how it goes, thanks for advice

keymatic, January 2012

if it was the cam chain that was loose it would rattle like hell especially on tick over but not really run any worse and also it would run bad on all cylinders if the cam chain was that badly stretched,i would say the problem was more like a weak running carb i would say that you should check the carb jets in no1 cylinders carb are clear as a weak running cylinder will pop and fart alot also the exhaust will get very hot and discolour.

adam bike doctor, January 2012