Can you put a throttle on a push lawn mower?
I'm trying to put my lawn mower engine on a bike. But it would not work right without a throttle. Currently my lawn mower is either on, or off. not slow, fast, etc. Is there a way to make it do that, so I can adjust speed?

Yes, You can buy replacement throttle cables in most lawn and garden stores, then you can connect it up to your carb.
There is an engine speed governor linked to the throttle; it is probably controlled by air pressure from the cooling fan. You may have to remove the flywheel to get at it. It can be disconnected, and a throttle cable attached to the actual throttle on the carburetor.