OS50-H tunning issue.

[moyesboy]

The problem was the throttle servo connector a little bit loose on the receiver. When adding vibration the servo would start failing. I had a spare servo ... Now it's all good for the weekend

Sounds like a good job it dodn't fly then!

Other things that can make an engine tick over but not open up fast:

Thin and weedy fuel line in the main tank that gets squashed flat when the exhaust back pressure builds up.
Loose baffle in the exhaust that blocks the exhaust when the motor gets going.

[Downdraft]

I had simular issues to yours with an OS37 and after reading an article in one of the heli mags about fuel tank lines discovered that my internal exhaust pressure line had collaped inside the fuel tank, so idle was fine but when the throttle was opened exhaust pressure increased and the pressure line was collapsing. It's just a thought but worth a look.