matchlessaero

Jason, sorry to hear that your radio was getting hit. Makes for an eventful flying day. : ( : ) : <}
We have the same problem at my field. Channel 38 gets hit particularly hard in a few certain spots around the runway and out over the farm over which we fly. The hits actually got so bad that I was forced to change all my radios off 38 (I had 4 radios on that ch)

Four particular things you can check on your engine. (These are the four factors that have affected me most while running Norvels and other Russkie variants).
You mentioned head shims- I experimented a bit with mine on Sat and Sun again and came back to the magic number of 2.
Second thing I have dealt with that affects performance (idle, transition and top end) quickly is fresh glow plugs. I change mine fairly frequently. I usually find that when my top end is suffering, and the idle is getting sketchy, the plug element is heavily aluminum fouled. Changing the plug quickly remedies that.
Third thing is Nitro Content- I am currently running 25% Sig, and I like 35% even better. I did not have hovering success with the 15% I ran through my HW.
Final thing is trash in the fuel. I try to run mine through a fuel filter to pull out the 'crud' as often as possible. (thanks to J. Leavitt for reminding me how important that is)

Why is this so doggone fresh in my mind? Saturday, I flew my Half-Wit, and it would barely maintain a hover, spins were suffering..... and I had to keep the idle trim 6 clicks higher than I like just to keep it running. I changed plugs and re-needled the engine, and instantly, I could readily punch right out of a hover, and the engine easily idled down low enough to rip off repeated touch-n-goes....