runs rough won't idle.

I recently bought a 2002 SW that had been mostly sitting for a couple years or more.
when I first rode it, it started good, idled rough, but reved up and ran good. When I would slow down to stop, it would snatch and jerk a little, and hold back more than I think it should. It stayed that way for about a 100 miles. I ran some seafoam through it. Yesterday I took it on a 90 mile run, and it progressively got to running rougher and by the time I had gone 50 miles, it started dying if I got below 20mph. Then it got to running rough and cutting out badly at 50 mph or more. I have not yet checked the air filter. Any ideas?

Check the air filter. Also the fuel pressure regulator.

Hi Yo wrote:

Check the air filter. Also the fuel pressure regulator.

The poor guy probably doesn't know what/where the fuel pressure regulator is, let alone how to check it.
A dirty air filter wouldn't cause the problems described, IMHO.

Start here:

https://www.silverwing600.com/t7339-oil-smells-like-fuel?highlight=fuel+pressure+regulator