Hi DenverJayhawk
I have three OS 46FX engines, about 8-10 years old. Recently one of them gave me the same type of trouble you are seeing. Then I noticed that the low speed needle valve, LSNV, seemed to have little resistance when turned. It was actually turning by itself when the engine was running. I replaced the LSNV and the HSNV with a set from a near new OS 46AX and all is perfect now. The engine starts instantly, accelerates very good, and has plenty of power. The engine still has good compression. I inspected the O-rings on the old LSNV and HSNV and they were in very bad shape. The one on the LSNV fell apart. I also felt grit on the LSNV. My new procedure now is to periodically flush out the cavity that the LSNV is adjusted through, with a squirt of fuel. I will also replace the LSNV and HSNV O-rings if there is little resistance when rotating them. Just ordered one set of O-rings from Tower Hobbies.