Ok so I know there could be several things here but need some help.

I took a new Aero LA 46 and bench ran it with a few tanks. Held a nice needle.
Bolted it on my Force and 4 flights went the same.
Launched at 9400 on 5/22 fuel in a clunk tank. No muffler pressure.
As soon as I pulled out inverted in the wing over it picked up RPM and never slowed back down when I brought it back upright. After flight #3 I moved the tank up 1/4 inch. Same thing.

I came home pulled the needle and blew air through it. Checked the filter- clean. Checked fuel by pushing some through a coffee filter. Clean. Looked into jug. Nothing.
Flight was done late in the late afternoon. 7:00pm so temp was very nice.
I do need to still check the hole placement on the NVA. I had to swap ends. But I figured if that was the problem would it no go back to the correct setting when I flew upright?

What am I missing?

OK:  I'm kinda regurgitating a lot of things I've heard from experts, plus some of my own experience.  Take what I say accordingly.

It ran away.  When it warmed up it could run at a 2-stroke with the mixture it was getting (essentially it leaned out).  Then the extra heat from combustion kept it warm.

Muffler pressure may help.  Or it may not.  It's worth a try.

Here are some questions that everyone will want to know, because yes, it all matters.

How much castor, how much synthetic?

What prop were you running?

What venturi size?

What glow plug?

Try the following things:

• Launch slower (richer)
• Get some panty hose; put one or two or three layers over your venturi.  This will act like a smaller venturi, which will give you more fuel draw and less air, and a more consistent run (and give you an air filter, to boot)
• If that fuel is all synthetic, try again with half-and-half
• Try an APC 12.25 x 3.75 prop.  If nothing else, it's what nearly everyone will tell you to use, so you may as well get that out of the way now

I just recently moved up to 40-sized airplanes after flying the "set and forget" FP-20 and LA-25 for several years.  It's traumatic -- it made me want to switch to electric, except I don't have the budget for such a huge change all at once.  I had what sounds like the same struggle you had, but I have at least one plane that works.  Here's what I'm running on my Fancherized, Hunt-ized Twister:

• Stock LA 46, with a metal backplate and a venturi
• Fuel is 8% nitro, 10% castor, and 11% synthetic.
  
  • Don't try to replicate that -- out of desperation one day shortly before a contest I just mixed some all synthetic fuel with some mostly-castor fuel that I had, and it worked.  It's a puke-green color, but I'm not arguing with its ability to fly my plane.  I have enough to last the year, then I'm experimenting with something off the shelf.  You can doctor your own fuel to get this mix, but you'll lose help if you do: no one will want to talk to you if you mix your own fuel.  Go buy something from Sig or wherever.
• Venturi diameter is something like 0.265 or 0.275, with an ST needle valve.  It has three or four layers of this lovely iridescent purple nylon net on it, providence unknown but probably not from around some nice lady's legs
• APC 12.25 x 3.75 prop.  Totally unmodified, but for balancing
• Hayes 4 ounce tank.  I'm currently filling it to the brim, but that generally gets me an overrun.  In competition I'll be pulling out 1/4 to 1/2 ounce
• Stock muffler
• Muffler pressure
• Sig 003 glow plug

What am I missing?

   If this is from Aero Products, all you may be missing is Randy's phone number!  Only thing I would have done different is use 10 or even 15% depending on the air density (which would let it run richer/cooler for a given speed) but follow the directions.

    Brett

In addition to the other suggestions I would ditch the clunk tank and go with a metal uniflow tank. If a clunk tank must be used try setting it up John Miller style. I have had some luck plumbing them the way he suggests and height adjustments can be made by moving the uniflow vent, not the tank. Details possibly here, definitely on the other site, search will bring it up. Good luck. 

Ok so I know there could be several things here but need some help.

I took a new Aero LA 46 and bench ran it with a few tanks. Held a nice needle.
Bolted it on my Force and 4 flights went the same.
Launched at 9400 on 5/22 fuel in a clunk tank. No muffler pressure.
As soon as I pulled out inverted in the wing over it picked up RPM and never slowed back down when I brought it back upright. After flight #3 I moved the tank up 1/4 inch. Same thing.

I came home pulled the needle and blew air through it. Checked the filter- clean. Checked fuel by pushing some through a coffee filter. Clean. Looked into jug. Nothing.
Flight was done late in the late afternoon. 7:00pm so temp was very nice.
I do need to still check the hole placement on the NVA. I had to swap ends. But I figured if that was the problem would it no go back to the correct setting when I flew upright?

What am I missing?

Lots of things could be happening, it may need more breakin time, The setup may have a vibration in it when it kicks into higher RPM, it maybe getting hot, first thing to do it run it some more, then run it on the plane and turn the nose up so it will pick up RPMs, look to see if the fuel is foaming, or if you can feel excessive vibration.
Make sure it is all solid in the mounting. lets us know how it is going

Randy

Lots of things could be happening, it may need more breakin time, The setup may have a vibration in it when it kicks into higher RPM, it maybe getting hot, first thing to do it run it some more, then run it on the plane and turn the nose up so it will pick up RPMs, look to see if the fuel is foaming, or if you can feel excessive vibration.
Make sure it is all solid in the mounting. lets us know how it is going

     I have seen cases where the nose would go into and out of resonance as the fuel load changed. The original Doctor seemingly had that problem with some engines.

    Brett

Dreaded profile bad vibe. Maybe. Inverse tetra tank. Has solved this on a few planes I know of. Buy a 20 dollar Tetra tank... then talk to Dan Banjok. It is rigged opposite to standard. Fuel is filled exterior to bladder. Bladder is evacuated (all the air is pulled out.) Then tank is fully filled, eliminating all air pockets. As the fuel is consumed the bladder expands, so there is no vacuum, and no air enters the fuel cavity, therefore no air bubbles. Fuel pickup is located in front of tank, since... (Ask Dan Banjok.) Try a small FP40 venturi, .256. Cut the 12.25x3.75 prop down 1/4 inch. Use aluminum engine pads. Use steel engine pads. Cinch the mounting screws real tight. Put a rectangular aluminum plate on the side opposite the engine large enough so that the 4 corners of plate fit the back end of the mounting screws. Run the mounting screws through the plate in the 4 corners. Cinch screws tight. Again. Minutely check the filter. How old are you. If you are over 50 have someone who is under 30 check the filter.

Actually sounds like the smaller venturi might help. Extra head gasket too. As the engine heats up it want to run at it's throttle (?) speed. The speed at which engine is in balance. Could be the engine is simply running in a comfy power band, determined by the prop, venturi size, and fuel. Engine might be fine, mounting might be fine, engine is just putting out too much power. Is there a lot of vibration as the engine is run on the ground? Is the fuel foaming? Two or three squirts of the new and improved original armoral might help.

I gave a thumb nail of the many attempts we have made to fix issues like the one described above. Interestingly enough all of the above have worked on one set up or another. Is the muffler free flowing? Stock mufflers can retain too much heat. Onward.

I like many others jump in and give it our best to diagnose engine run maladies at a distance. (An infinite distance? since this is cyberspace?) Unfortunately there are always many possible causes for poor engine runs. Almost impossible to fix stuff without being there, at the field, testing this and that solution. Which is why I scattershot, did a shotgun burst of off the top of my head. Recently my dead on reliable Magician Tower 40 powered profile became erratic. Leaning out. This at a contest of course, the Big B, where for many reasons I didn't have the time to figure out what was up. At home I got to fix the obvious that had loosened up over the years. But the probable cause was not clear until I took the filter apart (it's the small ones with a screen about the size of a cox reed valve filter) and cleaned it again, and then again. An almost invisible film somehow hardened over the mesh. Looking at it through a light source (my cataracts flashing) everything looked cool. No dirt particles, just a slight off color sheen. Poking a pin point through a mesh hole showed what had happened. New one on me. Very hard to clean off. I wound up fitting a different filter. Seemed like part of coating wouldn't let go.

SABATOGE!  You know who you are! 

I once had my XLS .36 suddenly fail to follow the needle (at a contest, on an official). If I opened the NV from its previous setting, it might run faster, and if I leaned it out, it might run slower or faster.  Keeping it running, I opened the NV way up with the glow ignitor still on, then leaned it back out, removed the ignitor, adjusted the NV, and put in my flight. Flushed whatever junk through the NV and through the engine. I don't suppose it will always work, but it's worth a try.  Steve