The top screw is normally the low screw,
but all engines are different and require different settings if you just take it off tick over and move the low setting screw slowly eather way untill it runs at its best its all done buy ear then put it on high revs but not flat out and adjust the high setting screw till it runs the best thats all i can advise but if not confident take it to local store which deals with them it dose not cost much about £10
lee, October 2008
