Swingin' too big of prop can also cause the engine to die after a few minutes under load. I have a ST75 bought new in early December and the guy at the hobby shop said to put 13x6 on it, so I did. Ran three tanks thru it on the bench with no problems, in fact it ran awesome. I put it on a Pheonix Super Decathlon 40, flew for about 3 minutes and it died. I landed and it re-started right away so I thought maybe air bubbles but no. After another flight with same results I read thru the manual and realized I should be using 12x7 or 8. I got a 12x7 and the engine runs perfect and hasn't died. It also seems to spin up smoother and faster while flying.

I definately agree with everyone else as far as running on the rich side but just something else to think about.

Scotty