I have a Yardman mower, self propelled electric start that does a nice cutting job but the self propelling is rather fast and it helps to relax the hold on the propel bar somewhat but it is very hard to hold the propel bar two inches down from the handle over bumpy ground. Even holding the propel bar lower doesn't really adjust the speed but merely lets the drive belt slip some giving the immpression of moving slower. It is a pretty poor way of speed adjustment. Any ideas on how to slow this speed demon down?