Go back to the original carb.

Assure that you have good airflow into and out of the engine compartment for good cooling. The engine will not be cooled by adjusting the needles. Through the engine is the best by installing a home made baffle. I'm with the group that thinks the engine was over heating, not going lean. Now set both carb needles to 1-1/2 turns open and start the tuning process all over again. Run the engine up to max rpm and peak the high needle. Then back off the high needle just a "skosh". Now drop the rpm down to about 3,000 or a little less. Use the low needle to peak the rpm. Check the high needle again by peaking and backing off justa touch. No numbers here, your ear will do. Now go fly and see if the low needle needs a little more adjusting. If it falters when you advance the throttle the low needle is too lean. If it blubbers it's too rich.

That wasn't hard to do at all now, was it?