Engine 1986 John Deere 318

Hello everyone!
I need to start by saying I am at the very beginning stages of learning about all the thing a you guys seem to know so much about.
I got a ton of help from this forum last week on my leaf vac.
Everyone around here wants to fix things for me and I appreciate that but I really want to learn myself and this forum has done that for me.

Now my problem... My family's 1986 John Deere 318 that sat in the weather for the last 25 years is not getting enough power. Seems full throttle seems weak.
If has the Onan engine and the gas in it is good.
So there you have it. Now let me have it!
Thanks for any direction or suggestions!
Phogan

Have you tried cleaning the carb?

Yes we took the carb out got it cleaned.
Is it an adjustment on the carb?

Short story.
This is the tractor I learned to operate when I was 10 years old.
It was my dad's and grandpa's and I would love to get it in shape.
Thanks for the help.
Phogan

See mechanic mark's link, that should answer your question.

Thanks!
Digging in tomorrow.
Phogan