Did the instructions manual come with the engine when you bought it used? If not, you might want to get a hold of a copy from YSPerformance.com. Then read the manual carefully and double check all fuel lines. Make sure the check valve is in the correct line and is facing the right way. 99% of YS engine problems stem from the engine operator. None of my YS engines are temperamental. They can be temperamental if you don't know what you are doing.

Here are some basic instructions: [link]http://www.ysperformance.com/html/instructions.htm[/link]

Then read this page: [link]http://home.comcast.net/~mark.fuess/ys110.htm[/link]