Well, this is the thread I have been needing to read for quite a while. My Hobbico Superstar came with a 40 LA. It started and ran beautifully the first few times it flew. Now it is running rough and quitting in the air after about 5 minutes. It is really putting a damper in my learning curve as I only get half a flight in. I did run it with a OS FS-40 four stroke for several weeks and that ran great. But that engine is now in another plane. Here is what I have done with the 40 LA: Dismantled and cleaned the entire engine, carb and needle valve, replaced the fuel tubing to the tank with larger diameter and a filtered clunk, and just last night I cut away at the plane to allow the tank to be raised up about 1/2". I was thinking I needed more fuel pressure. I was even considering getting a Perry pump. I have fiddled extensively with the needle setting and the air bleed. I have tried several glow plugs. I've tried running with muffler baffle removed.
Anyway, reading this thread I think my next steps are to check for leaks at the needle valve and carb. Unless anyone here would like a near new 40 LA on trade :-)? I wish OS would provide more in the way of troubleshooting, But then OS does have one of the nicest web sight of any other engine manufacturer.

FR