What you are describing makes little sense to me. I live at 5000' in Reno, and I have broken in literally hundreds of Jett engines for racers near and far, as well as sport engines. Never have I experienced a problem like you describe. Lets take it from the beginning. I will assume that this engine is new and has not been manhandled by anyone. Dub will test run all of his engines before he sends them out, so yours was fine when it left his shop. What glow plug is in it? I do not recognize the plug in the photo. It needs a hot plug, With the passing of Alton the only really available plug that is suitable is the Enya#3. What fuel are you using? Get a gallon of 15%, add 5 ounces of Castor oil to it, and shake it up. You now have suitable break in fuel. At your altitude it should pull a 10 x 6 at a healthy 17k, but that doesn't mean you can break the engine in on one. Put a 9.5 x 6 prop on it for bench runs. Pull the muffler off of it and look in both ends for any obstruction. If all is clean, check your fuel filter for blockage and leaks. Open the needle 6 turns or so, fire it up and immediately go to full throttle. It will spit and sputter, but if you keep glow heat on it, it will stay running. Lean the needle until it begins to clean up, pull glow heat, and lean it to a ragged 2 cycle. Pinch the muffler pressure line to lean it, and as it nears peak release the pressure line to richen it back up. Do this about once a minute for 4 tanks of fuel. At this point you can mount the engine in the plane. Burn the rest of the gallon of fuel you made, then add oil as necessary to your fuel to achieve 20% total oil. Never use less than 20%.

If the engine does not respond to this break in procedure, something is seriously wrong. Shoot me a PM and I will help you through it.

Scott