Originally posted by kane77
How can this have anything to do with the check valve? That doesn't make any sense to me. How does that have any affect on fuel dripping out of the carb? Something is wrong with the engine...
I have used many different fuels with it and it has been the same on each one, just small power differences. Currently I have been using YS 20/20 from Wildcat...
4*60, Just one more reason why I bought this engine... 
Just give it a shot, it takes 2 minutes to check it out, but I promise you that is the problem. You can have it up and running tomorrow or you can wait 2 weeks for YS to service it, your choice.
I dont understand exactly why this causes this problem but after flying only YS engines for the past 10 years I have seen it enough to know that fuel pouring out of the carb after shutdown is almost 100% of the time a faulty check valve.