Guys,
Having an issue with my El D - Fox 35 power. Engine starts great, set 4 cycle, launch then goes to rich 2 cycle. Fly OTS pattern, no sag, and after the vertical eights it starts to slowly come back to the 4 cycle. I have changed tanks from hard uniflow to round plastic double clunk uniflow, same run. Both tanks were air tight, no leaks. I have cleaned the nva assembly and found no trash. All the engine head and backplate bolts are tight, fuel is FOX fuel blend, glowplug is Enva No.3. Only thing I can think of is to pull back the pitch to 6 to 6 1/2 from 6 3/4" (9" diameter) to reduce the load a bit and let her wind up a bit.

Anyone have any other ideas or solution that worked?

Best,    DennisT

Use an APC  10.5x6 prop.  It is 'the bomb'.   TS

The concern with the APC 10.5x6 is the load with the muffler. Open face the 10 ish props are great. The muffler holds in some heat and the only way I have found to reduce that is drop to a lower 9" ish diameter. What is going on now is the reverse of the normal problem that occurs that being running a nice 4-2 at the beginning that breaks to a full out 2 for the last part of the pattern.

I have changed tanks from a hard tin tank to a circular plastic and got the same run. I thought the issues might have been trash in the spraybar that somehow floats out of the way after the overheads and allows the engine to go into the nice 4 cycle to finish the flight. However, I cleaned the spraybar and there was no trash. I have checked the engine bolts, all tight no signs of leaks. Crankshaft has no movement in the case. Engine turns freely without the plug, no binds.

My next move will be to go to the 9x6.5 prop then to a 9x6. The thinking is to again reduce load/heat to a more consistent level for the pattern and see if it will stay in the 4-2-4 mode (the reason I started going up in pitch was to get the lap time up a bit, this worked but I may have over done it). If that doesn't do it then I will change the plug to a new Enya No.3 and see if that does anything (current plug is an Enya No.3 that does not drop rpm when removing the battery at start, also looked at it no taters very clean). If none of this works I will order some all castor fuel and try that (I know some will say why didn't you try that first. Simply answer is I don't have any straight castor fuel, never used it and this engine ran fine with the current 50/50 fuel in the past).

Best,    DennisT

Went flying today and dropped the pitch to 6 1/2, and that seemed to be just enough load reduction to let the Fox run like a Fox. The lap time dropped a few tenth (pretty much expected that) but the motor run was solid from launch to end. Will go back to the 60 ft lines and that should get things were I wanted this ship to fly.

The idea I was working on was to increase the airplane speed, increase the line length (so you could keep up with it), to do this I tried increasing the pitch while keeping the engine running in a 4-2-4 run. The speed part worked (a little to good) but the engine run went sour as described at the beginning of this thread.

I have also tried the low ish pitch (5") higher rpm but the Fox was not happy at the higher rpm and was in a 2 cycle to get there, so I went the other. 

Best,    DennisT

Thanks Bob,
Now that I have it working pretty good, I can start changing things again to make improvements!!! I mean why leave well enough alone when we can have so much fun screwing it up then try to remember how to fix if again. Is that 10x8 a thin blade in carbon? See you at KOI.

Best,   DennisT