Hey guys I'm not making an airplane out of the motor I am trying to make so sort of rc truck so I think I would need some sort of clutch so it would idle without moving. If anyone has any ideas they would be appreciated.... Thanks

Hi,
I commend your effort, but you will need to spend time researching a gearbox to do that. I stand behind my Tower Hobbies reference, but it can become an expensive hobby. The best engines will be Kioritz, Stihl and Xenoah. Then you must determine rotaional direction, some run "backwards" compared to others. On the cheap some McCulloch and Homelite enginges suffice.
Modification is almost unavoidable.
Peace,
Clarke

Centrifugal Clutch could work.
You will need Brakes.