Cory, it certainly seems that the carburetor is part of the culprit, but your motor has sat for a while and the ignition may need looking into.
You can get a open gap spark checker at just about any auto parts store or on amazon for about $6 to $8 dollars.
Here is a video showing how to assess spark with an open gap checker on an 6hp Johnson. The process is the same for your motor. In the video it is hard to see the spark because filming was done in full sun light.
https://www.youtube.com/watch?v=p7w0xW48YCU
The next post below will have a lot of information, but please lets evaluate one section at a time. Let start off with spark. The rest of the information posted will be available for you to review as we go through the systems. Your grandfather’s motor has sat for a while, so it really needs a good evaluation. You can do it with guidance from the members.