Ive got a BlueBird rake with a 5hp IC Briggs motor. This last season I started having a really odd reoccuring problem with this one unit. It would run for a while warm up (sometimes not even warm up) then die. I had discovered mostly by accident that by adding small amount of new oil to the crancase the engine would start and run fine again. This could happen up to 5 times in a day. The unit doesnt appear to be burning any oil. I do oil changes on my rakes every day. Each spring I take the rakes in for servicing. Ive never had this problem with any other equpment. Any ideas??