RE: SK 90-----WOW
SK engines, even the ringed ones, have a tapered bore. All other ringed RC engines I know of have straight cylinders. Since the SKs are tapered, the Kangke techs told me to never, never run them rich. There is a break-in schedule in the instructions. As I recall, tank 1 is run at a rich 2-cycle, just after it breaks from 4-cycling. Tank 2 you open and close the needle valve from lean to rich every 10-15 seconds. Tank 3 you set at max rpm and back off 4 clicks, then you cycle the rpm from max to idle every 10-15 secs. Tank 4 is a full power run at max less 4 clicks. On tank 5 you set the idle, then run the rest of the tank out. They will also need a gallon or so of rich 2-cycle running in the air. Expect them to get better for 3 gallons. Sort of like a Saito. (At least mine) I have done 3 SK engines this way and all have run great.
I really like the SK carb. Before I go on, I never mess with the factory low end setting until after I run the break-in. Nearly every engine will run in a rich idle at the factory setting.
As I said, I like the SK 90 carb. I bought a Tower .75 and it had a very rich mid range. I could set the low end to idle for a long time, but the mid was terrible. I dropped on an SK 90 carb and the Tower ran perfectly. Tower did send me a new carb which works fine.
A buddy asked me to check his Evo .61 since the carb wouldn't adjust. I tried it on my bench and it must have an O-ring leak or something because it wouldn't hold a low end setting. Just for grins, I dropped the SK 90 carb on it. The throat diameters are the same. Ran perfectly. I am really impressed with the SK 90 carb.
SK 90s are designed for torque and not high rpm. A 14-6 will normally not run well. The transfer ports aren't large enough to pass the needed fuel for high rpm.
Yep, it's got anhedral!