Just two related questions:

1) Is it compulsary to have a Tach to tune a 4S engine? I havent actually flown my 91FS yet but have set it up by sound and a IR gun. Have set the idle just a bit above the point where the engine starts sputtering and it will surely speed up in flight

2) Due to model restrictions, the carb is below the tank, it is not possible to lower due to throttle rod routing. It is a good 1.5" above carb centre. Engine is inverted. Is that very critical?

3) On my veteran Top star model, the firewall actually deflects when going from idle to full throttle even with the engine off. You can actual see it deflect. I already tried resetting the throttle position but it doesnt help. There is no load on the servo at either end as there is no chatter or buzzing. Is this expected?

Ameyam