I have a strange problem perhaps someone has seen it before or has some advice. First I'll tell you the problem, then I'll tell you what I've checked/tried so far...

New plane with new engine (Ultra Sport 40 Plus with Tower .46). Engine was broke in meticulously and was running great for the first few flights. It's swinging a 12 1/4 x 3 3/4 APC. Running to max RPM then backing out about 1/4 turn on HS needle yields 11,700RPM. Now here's the problem.

The plane starts and runs PERFECT when sitting on the ground horizontal (in holding saddle). When taking off, and full throttle is hit, the engine will almost die (only with forward movement, not when it's stationary in saddle). If running in saddle, when plane is picked up at ANY throttle setting, once it hits about 45 degrees or less, the engine either dies, or if I'm running it VERY rich, it will increase RPM first, then die.

Now here's what I've tried / checked so far...

First thought was the clunk stuck in the front of the fuel tank. Though it hasn't had even seen so much as a rough touchdown. The clunk was riding about 1/4" off the back of the tank and everything is fine with it.

I tried replacing the glow plug, including trying one with an idle bar (since the engine is inverted), no results.

I tried richening the idle mixture, no results.

I checked ALL the fuel tubing for possible airleaks or holes, INCLUDING fuel tubing inside tank. No leaks found anywhere.

I bypassed the quickfill valve, just in case it was sucking air.. No results....

I pulled the tank and verified no cracks or air leaks.

I checked for any leaks around the crankcase or carb, nothing.

I verified that there are no kinks in fuel or pressure lines. Pressure line was hooked to muffler. Blowing on pressure line does force fuel out of fuel line. Made sure pressure fitting was not plugged.

Changed to a 10x7 prop (same one used for break in), no results.

And now I've run out of ideas... Has anyone seen anything like this before or have any idea what could possibly be causing it? Thanks in advance for any help!