I think the saw is an '04 and I am trying to find the gas tank vent. It is not in the cap and for the life of me I cannot find it. I looked at a schematic and it showed a check valve and cap but doesn’t show the exact placement. I just got the saw and the few times I have run it, it has been hard starting, but once started it runs and idles and once run starts easily. However, this past Tuesday I run it all day. I had started the day by cleaning the air filter and changing out the plug. After that it actually started a little easier and rev'd much higher and cleaner than before. As I used it during the day and put gas in it, I noticed that when I removed the gas cap that I would get a "hiss" like there was possibly vacuum in the tank. As the day was ending I was cutting a few stumps down to ground level when it started to struggle to stay running and evidently quit and I could never get it to restart. I let it sit a while took it home and I was never able to get it to restart. When I pulled the plug one side of the plug was a nice chocolate brown while the other was a lean white. I was thinking that a clogged vent may be the cause of some of my running problems near the end of the day. I probably ran three tanks through it and it ran great all day right up until the end. Any suggestions on what to check?