I installed brand new Kohler CH 668 in my mower. Motor does not start, fuel comes to carburator, but no fuel sprays into it. When pouring small amount of gas into carburator, it will run for a few seconds. tried to hold hand over carburator and after pouring gas and trottle at half speed with choke half open it will run on low speed for a minute or two. I know that it has solenoid shut-off, but then why would it run as described above?? I am lost?