I had my 250 rebuilt a little over a year ago and I only have maybe 10,000 miles on it. When you let up on the gas and you are going down hill blue smoke starts to come out and then when you start going again it stops. I thought maybe the PVC valve was sucking oil in the intake. I changed it and that didn't work but I still thought that had to be the problem and I finally just took the thing out and drove it that way and the problem is still there. Sometimes it doesn't do it. Here is what they did to my motor when it was rebuilt. They change all the valves in the head so it would burn unleaded. They change a sleeve that was cracked in the block and put in all new pistons and of course change the usual things. Please any suggestions and Ideas