Did you try running it in ES mode? Not sure if that would help or not. Many of these older Hondas(mine included) are a bit cold natured and don't like to run well until the engine warms up, especially when its cold outside. I think the choke doesn't work properly on my Rancher ES so I basically just have to start it and feather the throttle for a min or 2 before I put it in gear and try to take off but it runs and idles fine then. My friends 300 fourtrax was running rough and had trouble starting it and he replaced the coil wire and plug and it runs great now. If its misfiring, it probably at least needs a new spark plug, it wouldn't hurt anything for sure. The coil wire could have been knocked loose when you were wrestling your Rubicon from the tree, maybe making poor or intermittent contact now. Something to check anyway if you haven't already.

 

I will check out the carb, id be shocked if it was clogged as im pretty **** with my ethanol free fuel with stabil and draing them when in storage for extended periods. Plus it runs perfectly at every throttle position when opened up- something a clogged jet wont allow- Will keep ya all updated.

 

FIXED- I phoned a old friend who went to MIT, he watched the video and said the fix takes under a minute- he had me pull the diaphragm out and spray it and the slide with silicone, drop it back together and test ride- worked great! He says that the reason it ran fine at high RPM was that the increase in vacuum allowed the slide to move but at lower RPM it kept sticking and cutting off fuel. He says this is common when stored and people always over think the issue.

 

Good deal then, always nice to find a cheap and easy solution. I took my Rancher out today and played in the snow around here and the starter even worked, didn't have to pull start it like I had recently so that was a plus. Once it got warmed up it ran great. Its only 2wd but it went through the 8-9 inches of snow just fine. I finally got it stuck when it got high-centered by the edge of the road where it had been plowed but I was able to put it in reverse and push it out. Usually it takes off just fine in 2nd or 3rd gear but I had to take off in 1st to get it going in the snow, needed the extra power to plow through.

 

The 500 Honda models do give trouble with the CD piston. I have known them to stick and to wear excessively. It doesn't seem to be a problem on the smaller engines, so I suspect a design fault with the bigger carb fitted to these models.

 

Yup, I did notice that the throttle body was coated in microscopic particles of whatever the slide is made of. Easy enough to replace though, and just like my friend said- 4 screws and pull. 1 minute