Hi aString. This is Joe in Chandler. I have had a mounting bolt shear off about 5 times now. In my case I think it has to to with rough road conditions. I was able to go to ace hardware and get the 1/4 20 grade 8 bolts and nuts. I had to file the closest to the engine though. I have about 1200 miles now on my GEBE 35cc. Hope you have better luck than me.
You have to tighten them down really tight. It was my fault that it broke (I had it to loose). You should check that bolt and tighten it down.