I'm having trouble keeping the prop mounted properly to my E-Flite Park 250. The motor comes standard with a prop-saver and I'm using an APC 8x6 SF with the larger prop adapter. The problem is when I throtle up the prop stays on the motor but slips to the side. I'm using two retaining bands but that doesn't seem to help.

AUW is 7.5 oz.

Are there any other mounting options for this motor? Supporting pictures would be a big help as well.

I'd be looking at the prop to mount fit. Almost sounds like the hole in the prop is too big for the mount, alowing it to walk off of it. Also if you can, slide the mount back a little so that the motor shaft sticks out slightly, this will help keep the prop from rolling off to one side of the mount.

Prop is ok isn't it? Checked for balance, no damage like a bent blade or such? A bad prop can cause all kinds of problems.

What else? Umm even double O rings may be a problem if they are weak. Some of the ones I've seen coming with prop savers barely have the strength to hold the prop in place when it's not spinning. And for that matter O rings do loose their strength, they stretch out. My practice is to remove them after I'm done flying, and give em a good once over when I reinstall them.

A spinning prop wants to move up and to the left as it spins, so weak O rings may allow it to walk off the prop saver.

Lastly, a bent shaft or mount could be causing this. Some of these prop savers don't have a tight clearance between the motor shaft and mount bore, allowing the mount to rock back and forth as it's spinning. And any vibrations from a bad prop will magnify this condition. At speed the props going one way and the mount is going another and next thing you know the prop jumps off the mount.