As posted by reomack, it sounds like you need to do more than adjust your carb. It sounds like you are not familiar with carbs. If you don't have the service manual for your tractor you should get it. It has good info about servicing the carb. You should have at least a basic carb kit, spray carb cleaner, and a set of torch tip cleaners before you start.
In case needed, always have the data (serial number) plate info at hand when ordering manuals and parts. AGCO Publications is the OEM source. You can use the phone number at the upper right if you want to talk to a person to be sure you order the right manual. http://www.agcopubs.com/default.aspx?model=135&brand=44096&keywords=135&language=44415&mediaType=&category=44280&searchForm=1
. The YT store likely has some manuals for your tractor. I would get an OEM or reprint of the OEM manual first, before getting an I&T manual. eBay is a source for used OEM manuals and reprints.
More detailed help will be available here once you decide on your course of action. General consensus is generally to overhaul your carb, not replace with aftermarket, except as a last resort. There are some fellows on here you can send you carb to for an overhaul if you don't want to tackle it.