Dave, I will start with not all Norvel engines are the same. Knowing what version you have isn't a necessity but it could help. Not all Norvel engines require high nitro fuel. They can do exceptionally well on just 10%. However, when you run bladder, it's nice to offer slightly higher nitro as it assists in needling. I use the  Cox 5x3 for a .061 Norvel on bladder. Many times, I even have it cut down to as much as 3 7/8" but for the most part, I use 4 1/4- 4 1/2".  The .049 being smaller and while the 5x3 isn't a bad choice when running suction, running bladder doesn't generally like a load. You might want to try the APC 4.6x3, it's size and narrow blades might just work well as I use this combo on some of mine.

                 I see your aware of the Revlite version due to owning one. The reason I asked about what Norvel, some are Revlite and some are ABN which I've found that some swing the full prop while others like it clipped. The AME version vs the Big Mig also changes the equation. Big Mig versions can run less nitro and offer substantial power but the AME the higher performance version I've found requires higher nitro . When I use lesser nitro on the AME, the plug likes to cool off and I get anything from shut offs to sporadic running. I've also noted that the AME doesn't like the full size props compared to the Big Mig.

           I would certainly offer less nitro on the Streak to try it and if you find is satisfactorily running, I would add another head gasket and try your higher nitro fuel once again. In general, I've always found 2 Cox head gaskets to work under my Nelson heads using 10% nitro once the engine was broken in.

          The crankshaft rides in the aluminum case. The front portion of these shafts always tend to pick up aluminum and gall the case. The fragments of aluminum embed themselves on the shaft. I like to remove the shaft and polish them up using fine paper 400 -1500 grit. This tends to eliminate any drag and overheating issues that sometimes occur.

       The other thing I have to inquire about is that are you using the venturi assembly with the KK spraybar? I lose the venturi and press the spraybar directly into the case leaving the gaping bathtub shaped opening. Point the hole in the spraybar directly down into the crank window and this offers some more power.

       


     

APC came out with the 5.7 x 3 about the same time that the Norvel .049 - .061 came out....hmmmm...

The first generation Norvels were very tight and need to be broken in with 25% to 30% oil content fuel and a small enough prop to allow 22000 rpm [or more] without being fully leaned out. You want to the engine to have a "slightly rich scream". An  APC 4.2 x 4 works for this, or cut a Cox 5 x 3 down to 4.5 x 3. The idea is to get the cylinder expanded quickly to relieve the interference fit between the piston / liner and let these parts "break in" at a high RPM, but without getting too hot.
The "loaded down" deal can be from gunk / slurry that needs to be removed from the crankshaft bore.  Disassemble and clean with a gun cleaning kit, then test the crank fit by flicking a prop, it should spin for several seconds after normal effort "flick" and never stop abruptly. The crank can be polished with a paste made with sink cleanser and oil. Never work on the case, just the shaft.
Some Norvel / Cox owners disassembled and "sonic cleaned" their engines before they were fired up for the first time.
The Revlite Norvels I've owned were much more ready to run [than the 1st Gen Norvels], but I've always added SIG caster oil to the "store bought" fuel, which for me was usually Powermaster 15% nitro.
SIG sells fuel with the extra oil content. I believe it's got 25% oil.
Extra oil allows for more aggressive needle settings. I've never traced a premature failure to running too much oil.
With a piston going up and down 400 times per second, everything about these tiny engines is so critical.

Solved

I just ran it with a cut down 5x3 rubber duck.  I got the rework instructions from brother tom. 

He claims to have won the nats with a prop like that in 1/2 combat.  He used a fora with a cutdown cox prop, and never broke one all day.

1) cut off about 3/8 of an inch on each tip

2) trim about 1/4 of the Leading edge of the prop at a 45 degree angle.

It looks pretty strange.

So its a little over 4" with the LE clipped off on a 45.   it looks comically small short and fat. 

Think I will make a few more. 

On 10% it started and held a needle in slightly rich or screaming for a whole bag, ran great. 

The needle did not change.  I could go from rich to lean. 
 

Here's a site describing many high performance small engines .049-.061 .
 http://www.gregorie.org/freeflight/f1j/index.html

Cutting down the cox is one answer or go to a 2 pitch russian glass prop but it sounds like you've solved your problem.

yes the Russian props are better, but they don't like being stuffed into the ground, they snap.  The rubber ducks live on.

The good news is he motor is OK and I can fly it.  I'll save the glass props for when i get a fora.