Open the main needle to make the engine run slopy rich.
GET A TACHOMETER
start over on adjusting the engine... and find peak rpm, then richen the mix for a 400 rpm drop.

Double-check for any pinholes in the fuel lines, including the clunk line inside the fuel tank...

It could also be an overload propellor... Too much prop will make 4-strokes do wierd stuff.

Did you goof and offset the valve tming when you had things taken apart?

If you are running a tuned pipe... you may have the pressure tap in a location that pulls a vacuum at higher throttle settings... that will make the engine either surge or kill it at high throttle. (I found that out the hard way...)

(I'll bet on the first suggestion.... If its lean... it surges.)

How thick is the white smoke comming out the exhaust? (at high throttle)

If its thick and very easilly seen in flight... you're rich. If you can't see it at all against a CLEAR blue sky, you're lean.

I'm betting you're on the rich end... this causes the engine to spee up as you enter a loop, peaking just before you one on the vertical downline, and then act like its going to die just as you level out. (full throttle the whole loop) The exhaust trail tapers to about what it should look like all the time about the top of the loop.

It is also possible that the engien simply doesn't like that 11X7... On my .91 I noted a full turn difference in needle setting changing from a 14-8 MA wood to a 14-6 APC grey nylon Pattern prop. The engine surged(as in the rich in loops description above) with the 14-8, and is rock steady with the APC. Leaning more with the wood prop made the engine overheat... so it was too much prop.