I,ve got a Brison 5.8 single engine that is giving me fits, to say the least. I have been around the block and back with this engine with no end in site. I get it to start fine and runs at idle good. Has real good transition to full rpm, but when I get it in the air it starts to run rich at around the mid throttle position and will quit the second you pull it to idle. I have tried two dozen mixture settings already and have even closed off the regulator port with some bass tubing and ran the regulator back into the fuse with some fuel line. This engine runs great at full throttle and has lots of power but anything below half and it's just crap!!
I am out of options.. I have 8 other gas engines that run great and were easy to tune, this just blows my mind. Please help if you have any info.

Thanks