G day,

Have had simmilar problems, firstly what is the engine cowl like ? we have been having a lot of trouble here in Australia this summer with in cowl heat which could explain why it runs on the bench ok. Make shure you have twice as much air out as what goes in. I have also had to install a heat shield between the carb and muffler on a couple of war birds I have to prevent vapor lock.
My starting point for both mixture screws is roughly one and one half turns out. Could also be that your high end is too lean, this will definatly cause it to die especially if there is a over heating problem in the coul as well.
Does it stumble as you go from idle to full noise? this also is just practice in tuning. I have been running 18 x 8 2 blade Master Airscrews but have reciently found 18 x 8 Bamboola props far more effecient and easier on the pocket.

Regards
Noel