Welcome,
In order for us to help you, be aware that we will need the make and model along with the product label information off of the machine you are having trouble with.
If it is engine related, we will need the label information or the stamped numbers in the valve cover if B&S. The machine manufacturer does not usually make the engines on their machines.
The more machine information you can provide the better. There are way too many differences for us to take guesses.