RE: Telling difference between Nelson Q40 LS & Q40 SS
Run it on 15% nitro. What looks to you like a carburetor is not. It is a choke only. It does not have a low speed needle. The engine will not run below 12000 rpm and probably not below 15000. It will just flood and shut down. That black thing is just for shutting the engine down at the end of a heat. It can also be used for dropping the rpm to about 16.5 to 17 on the start line to keep the engine from over heating. The props you have I would worry about using. They are not designed for the power and rpm this engine will put out and may break. You need a pylon prop. 8.8*8.75 or in that range APC. With this prop this engine should run in the mid 19s. Dub Jett makes or used to make a carburetor that fits that engine nicely and works quite well down to 3000 rpm.
Denis