Some backyard testing:

After 6 liter of fuel, I couldn't get the engine to accelerate perfect like it did before. I removed a 0,2 mm headshim, and that solved the problem. Like HPI suggests, the standard 0,8 mm headshims are for 25% nitro, so a total of 0,6 mm shims fits my 20% fuel great.

6 mm vs 8 mm venturi:

With JP-3 pipe, 6 mm venturi and 20% nitro, the engine runs very well. Nice bottom and a ok top (33.000 RPM).

Then I put the stock 8 mm venturi in the carburator. I had to turn the HSN 7/10 of a turn OUT, to get the setting right!!! The bottom became less aggressive. Actually it sounded like too soft clutch springs. The top rpm was now 34800 RPM.

Next was my Dynamite 086 pipe: The HSN was very rich, and I had to lean it nearly 1/3 turn! Bottom was a little better and the engine got 35400 RPM at WOT.

Last up was Novarossi 9901:
Very similar in performace with the 086. The big different was the tuning. Had to lean the HSN 1/4 of a turn, to get it right.