RcKrazy
If your 7lbs plane is a trainer and is rated for a 40 size engine the Magnum 40 will fly it just fine. But if it is a sport plane you engine will not be up to it. What 7 lbs plane are you planning on using with your Magnum 40? And is you magnum 40 a GP or an XL model. You have a little more power with the XL model.
Thanks