Hello Max, Thank you for your input. Since i wrote the post i have spoken with a mechanic at our local mower dealership, and he has suggested there may be an issue with the valve seats coming loose. In all my time playing with engines i have never heard of this happening. Have you ever heard of a valve seat letting go in this manner?.......at any rate it looks like i'm going to have to pull the engine down and have a good look through it. That job will have to wait as i need to fix my own mower as per the problem described in my 1st post.
