I'm still trying to work out whatever my new Fuji is / is not doing. I have almost a gallon through it now, it still cuts out/misses above half throttle. I've been working on the assumption that the problem is fuel related, as it sounds like lean running. This is what I've done so far:

Using a MA 18-6 Classic prop, and Amsoil Saber 100:1 oil. I started out at a rich oil ratio, 32:1, because this was the Fuji manual recommendation for non-Fuji oil. At 32:1 the engine would hardly run, lean or rich, and had lots of black goo out the exhaust. I ran two 16 oz tankfuls like this, wouldn't go over 4000 rpm. I leaned the oil mix to 50:1 on the next tank, and it was a bit better, plus I could lean the needles a little, but there was a point where the engine would start missing and cutting out above half throttle. I thought maybe I was having a delivery problem, so I changed things in the fuel line; I was using a "T" fitting in the line from the clunk to my fill line, thought maybe it was sucking air there, so I changed to a 3-line system, no improvement. I changed from a filter clunk to a non-filter clunk, no improvement. I re-routed the fuel line, thinking maybe vibration was causing some foaming in the fuel line, no improvement.

I thought maybe the switches were vibrating, causing intermittent electrical interruptions to the ignition. I eliminated both switches from the setup and wired the battery straight to the ignition, no improvement (fully charged, 1450mAh 4.8V NiMH battery).

The engine is incredibly easy to start. Choke closed, flip it 3-4 times, cut on ignition, flip twice, it fires. Open choke, flip 2-3 times, it fires and runs smoothly at about 1900-2000 rpm, and once warmed up, will idle at 1750. Blip the throttle, no hesitation or gurgling, and it revs to about 3000 before things start happening. I've tried leaning each needle, and then once idle and transition start suffering, I richen the low end and think I have it set where it needs to be. The high end, I richen until it won't take throttle but just gurgles and dies. I lean the high end, and the running improves to a point, rpms will go to as high as about 7000, but it is still too rich. I tried flying the plane at this point. It took about 250 feet to get it off the ground (1/4 scale Decathlon) and climb out was slow; the engine just wouldn't make decent power. I managed about 5 laps around the field to trim it, and then landed. The whole time I was in the air, I was at 2/3 to full throttle, and it was missing and cutting out the whole time.

If I lean the top end any more, the midrange will improve and get smoother, but the missing continues from around 4500 on. If I continue to lean out the top end, it finally stops running. Total screw movement from blubbery rich to leaned out quit is less than half a turn. I have checked the screen in the carb and it is spotless. I ran the tank dry, and the last 10 seconds or so, as it burned up the remaining fuel and leaned out , was solid and smooth, and I'm guessing the engine was turning over 8000 before it quit.

I'm about at wits end with this thing. My gut tells me it's a fuel related problem, not ignition, but a couple of guys at the field think it might have something to do with the electronic advance. I don't know of anyone near me with this engine so I can try their module.

Could there be a problem with the spark plug? It works fine throughout the low and midrange, and on a couple of brief occasions, very smoothly in the upper range. I don't think it's receiver related glitching, I'm using a 2.4 GHz (Spektrum), the receiver is 14 inches from the EI module, 16 inches from the spark plug. All my control surfaces work consistently and correctly.

What, What, What,WHAT!!! is it?