Thank you all for your input. I will switch to 10x5s for the next flying session and see if I can find some 15% Omega. I'm sure the onboard glow would help, but I hesitate to add the weight of 3 systems to an already heavy (and nose heavy) airplane. The same for the spinner weights. The larger props will add some flywheel weight.

I tried the 9x6 props because Hobby People recommends it, but after running them, I think you are all correct that the 10x5 or 10x6 is a better choice. Can anyone tell me, from experience, whether the 10x6 (more pitch) will fly the airplane faster or slower than the 10x5 (more rpm)? I'm looking for slower, since that would be better for the JU 52.

Ed Cregger: I have three separate throttle servos and the throttle arms are visibly steady while the engines are running. The surging is not caused by the throttles. I think overspeed and valve float are more likely, which the larger props should cure.

Jim