More info would be helpful, but if the fuel system is set up correctly, the most likely cause of deadsticks is that the engine is overheating. That can have a number of causes.
1. Not enough air flow around the engine
2. Engine is being run too lean
3. Engine is being over proped
Here's a couple more links on setting up and running YS engines.

http://www.probuild-uk.co.uk/factsheets/ys_engines.php
http://www.patternflyer.com/troy/?page_id=13

Hope that helps,
Paul