My rover mower backfires through the carby it runs for about 10sec and then stops would this be a valve problem.the compression seems good.

Hi,
Generally this is an ignition timing or valve problem. It also might be wise to include the fact that it is an Austrlian mower though it is a division of MTD.
Manuals: Rovermowers.com.au/Page/Info-Centre/Owners-Manuals (http://www.rovermowers.com.au/Page/Info-Centre/Owners-Manuals)
Peace,
Clarke