a duff battery could cause some weird symptoms, so how is it running now with a new battery? if no better then you could check for correct grade of spark plug, if OK then clean and set the gap correctly, check oil levels are OK, electrical connections are clean and tight, the plug cap and lead fit tightly & are in vgc. make sure you have fresh clean fuel flowing to the carb & the petrol tank cap breather is clear(if blocked could cause a vacuum in tank & restrict flow)
Chris P.Duck
October 2010