I bought another one, SK .91, that is. Even though the price went up to $100, the Magnum .91XLS is $150 (I also have one of these) and the OS .91FX is $210 (I did own one of these and sold it), so the SK is still a bargain.

My first one is running perfectly. I have not seen any of the maladies reported in another SK thread here. Today, I flew around at half power for 3-4 minutes, then hit the power and it went instantly to full throttle, no hesitation, no smoking, no stumbling. I have probably over a gallon and a half of fuel through the engine and it is running very strong, pulling a trash can, over 8 pounds Ultra Stick vertical as long as I want. I have not used a started on it. It normally starts in 1 back flip.

I did break it in per the instructions for the 5 tanks of fuel, 1: rich 2-cycle, 2: rich-lean cycling, 3: high low throttle cycling, 4: 4 clicks off peak run, 5: set idle. I also ran several flights at a rich 2-cycle. Maybe it's the castor blend fuel I use (Omega 10%) or maybe it's that I set my engines to leave a slight smoke trail, but I rarely have a lean run or engine trouble.

I am running a 15-6 prop, which Ray Nano from SK Engines Tech Support recommended. He said a 15-6 (minimum size) or a 15-8 so I am running a 15-6 Master Airscrew Scimitar. I know I ought to order an APC 15-6. The prop looks big, it doesn't scream, but it pulls like I don't know what. I had to buy another SK .91 just because this one is running so darn good.

I ran the new one on the bench this afternoon, doing the break-in. 5 tanks. Zinger 15-6 wood prop. I have yet to adjust the low end mixture on this one. I let it idle for 1-minute and 10 seconds, timed on my watch. I popped the power and it went to full throttle, no hesitation. That is hard to beat.

I don't know what rpm it runs because, even though I have a tach, I rarely use it. I can tell how an engine pulls a plane and this one pulls to my satisfaction.

I know some people are having trouble with this engine. Maybe they didn't break it in as stated in the instructions, but used their old standard break-in or what some local expert told them. Maybe they are running a smaller prop. I would normally use a 14-6, but Ray says it won't run well. It will go lean in flight. Why argue with the guy who was in on the design of the engine. I am running the big prop like he said. My 2, and the 50 I also bought, run great.