My yamaha szr 660 will not start ,the only way to start it is to remove tank ,air box and cover the end off the carbs with the tea towel,photo three.starts right away. Been to the dealers they cleaned the carb and adjusted the valves.was ok for a week .not started for a week ,back to square one ,not starting.new plug and the bike as only done 3500 miles ,( probably because it will not start) two owner me the second ,it's mint,that's it folks ,help wanted ,any ideas?