Hi,
Forget about that battery, not big enough.
You need to measure some voltages.
The throttle arm is probably pretty free when the engine is not running, but if you advance the throttle while the engine is running there probably will be a back force.
Unless you have power steering there will be forces coming back from the steering mechanism too.
You need a much bigger battery.
Can you post a picture of your project so we can see your component layout.
A hand drawn circuit with labels on pins would have been better, fritzy pictures are just that, pictures they very rarely show all the information needed.
For example are you really using a protoboard?
Thanks.. Tom... 