RE: 90 lx?
Sounds like you did not complete the bench run before installing the engine in the airplane? Do not skip that .... its important for the engine, and is also important so you understand how the engine runs.
The LX engines are specalty engines they come with special instructions. These engines run great, but they require full knowlege of how they run for you to be successful.
Test bench - 11x7 prop at least 20 minutes. You want the engine at 14,500 rpm it will do this, running rich a bit with the 11x7. You want the engine running at its intended rpm - you do not break this in slobbering rich like a ringed engine or 4c. This gets the engine some time on it in the right conditions, and it ALSO allows the operator to understand how the engine works, approximate needle positions, and gives you baseline RPM info under controlled conditions.
If you require, I can send you the break-in proceedure.
Running at 11K rpm is WAY off of the pipe and is not doing the engine any good.
Important to note, "number of turns" on the needle means little/nothing. We provide reference to start with, but each installation will result in a different setting. I have one SJ-50 engine that sets up around 5-6 turns out... works properly. Ensure that that packing nut on the needle is snug so the needle takes a bit of effort to rotate.
Also........
The idle needle is pre-set at the factory. It is not a "normal" idle mixture. It is more of a midrange mixture. If you can, reset it where it was to start with. You do not want to "tweek" it more than 1/8 of a turn from where Dub had it set. If you are not sure, I can help you with a proceedure to reset this.
Start over a bit.
11x7 prop for break in, and the first few flights
Target 14,500 - 15,000 rpm find peak rpm on the engine (Briefly) and back off 600-800 rpm for flight. If you do not have a tachometer, see if you can borrow one. For this particular engine you pretty much need it (at least to start with until you know what it sounds like )
After a few flights go with the 11x8. Same thing. Find peak rpm - somewhere around 15,000 rpm as a reference then back off 600-800 rpm for flight.
If the opportunity permits, send me a photo of the aircraft and installation.
With this engine, fuel foaming is a real possibility. A lot of energy output. Make sure your fuel tank is 100% isolated in foam rubber and is not touching any of the airframe. Fuel foam will drive you nuts.
Bob