Originally Posted by r00t4rd3d
What directions are you following ? Do you have the spark plug in the engine ? It wont turn over very easy if it is in.
Installing the rear sprocket is the hardest part I think. At least it was for me when I first did a bike. You just have to take your time.
Do you have the coaster brake arm off ? The directions say to file your rear sprocket to fit but its easier to just trim the dust cap. More accurate too.
You said you cut the rubber "pieces" , you only need to cut one. One goes on the inside and one on the outside.
Here is more instructions with pictures :
Center Mount Gas Motorized Bicycle Plans Installation
Some of those instructions in that link are off, in step six for instance, you only need to cut one of the rubbers so it can go inside the spokes. Modify your coaster brake arm and also make sure that the chain tensioner is secured so it can't rotate on the chain stay and wipe out your spokes. (drill a small hole through the tensioner into the chainstay and install a selftapping screw) Better yet adjust the motor chain tension correctly and use the tensioner on the other (bicycle chain) side.