80cc motorized bicycle top speed… ???

Something happened to the top speed after engine kit break-in today. The kids bicycle motor was slower than the 20 I was expecting, and sketchy as heck! The top speed was 14.7 mph. I feel I had a faster run before, but I am on a rocky road and it’s hard to keep the bike strait at higher speed.

Any ideas why the good ol 80cc’er slowed down?

I could break the tire free, but the training wheels prevented a full sh**ywhippin’ good time! .