first off, welcome to the site
when you say oil is dirty, , do you mean has a few miles and hours on, or , was it suck and sucked in dirt??
two totally different things LOL
and sounds to me like, you MIGHT need to find someone with a programmer and turn up your idle!
I am sure you DON"T want to hear this, but running 28's on this atv is sure not being kind to it!
Ranchers geared higher than other honda 4x4's, now on full sized frames and that's asking a LOT of a small HP motor!
long life isn;t going to a deal here, just so you know!
NO offence meant, just honest info!