ORIGINAL: Ed_Moorman
The SK .91 will pull it, but you must break it in first. I have one right now in an Ultra Stick 60 and it pulls quite well. It is going to take about a gallon of fuel before you will be able to get good adjustments on it. I followed the instructions in the break-in which takes 5 tanks, each one run differently. After that you fly in a slightly rich 2-cycle. At about 3/4 gallon the idle will come around.
Even though it is a ringed engine, it has a tapered bore like an ABC engine and must not be run in a rich 4-cycle.
You must use a 15-6 or larger prop. The engine is a torquer and won't run well on smaller props. 11,000-11,500 rpm is the max it is ported for. If you want to run higher engine, you may as well get another engine.
For inverted installation, I would run an OS Type F or a Fox Miracle plug. Both have an extended tip which should help keep excess fuel from pooling in the plug, putting it out. With any inverted engine, a well broken in one works best. Put a brand new engine in an inverted installation and you are asking for trouble.
I would recommend getting a Stick or some other 60 size plane to fly it in until it is ready for prime time. And do not listen to the local gurus who tell you to use a 14-6 prop. It is an excellent engine when broken in correctly and run as it was designed. Mine has not missed a beat in the air, never quit, never kicked me and I hand start all the time, never failed to cut off after landing. Unfortunately, some people will drop it right in a plane, not break it in or run it slobbering rich and put a 13-6 or 14-6 on it and never get any useful time or fun out of the engine.
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You're not being fair to the local gurus, Ed.
Experience gained over many years of flying says that .90 two-strokes run best with a 13x8 to 14x6 prop. Then comes along SK with their different port timing, etc., and this upsets the apple cart. How would anyone know about this lower tuning by looking at their advertisement copy?
By the way, I just ordered one of these SK .90s so that I can experience the lower rpm power band of this engine. It sounds like a good idea, especially for those flying 3D these days. Also, I've been on a low rpm two-stroke kick for a while and have been collecting old OS.61SF engines, for just this reason.
So, I'm not bad mouthing Kangke, or saying that the 15x6 requirement is not true (I'm being educated too), but you have to admit that before this engine became available, the vast majority of .90 sized two-strokes did utilize props that would permit the engine to rev up a bit higher.
We're just talking here. No offense of even the slightest amount is intended.