It may be that the muffler is clogged with oil sludge. Simply undo the bolts that hold it on and then flush it out with petrol till clean.. let dry then reinstall.
Also I would replace the plug under suspicion as it may have a cracked insulator which may be so fine as to go undetected.
Good luck!
Mark M
January 2009
howtomendit.com for free repair help, information and advice.
