The SK line of engines are ported for lower RPMs and swing a bit bigger prop then normal. I haven't got an .80 but I fell in love with there .90, super duper engines. I bought my first one right after Ed Moorman did a report on them in RC Report a while back. The manual did state some wrong prop sizes and Ed contacted the factory rep. and was given some better information about the engines. The .90 likes a 15X6 prop to start with then you can try some different props until you find what you like. I use the 15X6 or 15X4 props on mine. If you go to the glow engine forum there were/are a number of people that were talking about these engines. Set the needle like Minn said but remember, these engines do not like to run too fat. Ed wrote about them in Jan. of 07 and it's worth the time to try to get a copy of his article. My scanner isn't working or I could send it to you by email. If you can't find it then ask me and I can send you a hard copy of it.