Dalton asked: Are there restrictions on what size of engine you can put on a bicycle or tricycle?
That depends on what you are trying to accomplish. If you want the vehicle to remain a bicycle and not register it or have a driver’s license, it must meet the following statutory definition of a bicycle.
s. 316.003 – Definitions
(4) Bicycle – Every vehicle propelled solely by human power, and every motorized bicycle propelled by a combination of human power and an electric helper motor capable of propelling the vehicle at a speed of not more than 20 miles per hour on level ground upon which any person may ride, having two tandem wheels, and including any device generally recognized as a bicycle though equipped with two front or two rear wheels. The term does not include such a vehicle with a seat height of no more than 25 inches from the ground when the seat is adjusted to its highest position or a scooter or similar device.
Note that only electric assist motors are permitted in that definition.
If you want to use a gasoline assist motor on a bicycle, it must be registered as a moped and requires a driver’s license. See this post.
See the embedded link for the DMV Procedure RS 68 for the details.
If you want to have a higher-powered engine, either gas or electric, the vehicle must be meet the requirements and be registered as a moped or a motorcycle.