I've never had a problem with idle on any engine so far. With my test engine (an Enya 60X) I found I had to lean out the idle mix considerably and then close the barrel further to get the idle speed way back down because the higher compression made it much more efficient at idle speeds. It then idled much more smoothly and lower than it did as standard. I had a 20% increase in HP on the same prop, fuel and plug calculated from the rev increase. The other thing I noticed was that the engine unloaded far more in flight.

Actually, when I did the experiment I wasn't sure what compression I'd end up with or if I'd be able to skim enough from the standard head to go high enough without getting too close to the piston so I made a new head with a slightly smaller combustion chamber. But before doing that I figured out how to make it a variable compression as well so I could then alter the compression while it was running to get an immediate change in revs. I couldn't alter the compression at full throttle because there's too much pressure inside the engine so I had to back it down to idle, make a change, then go back to full throttle. It worked so well I just left that head on the engine to go flying .